Direct answer
For the Samsung Galaxy S24, carrier service, selected line, account activation, recipient-specific block and messaging service should be separated. First, test a normal call, SMS and another contact with Wi-Fi off.
What this covers
- Samsung Galaxy S24 (SM-S921*)
- Samsung Galaxy family; S Pen, foldable display, DeX, USB moisture and One UI features vary by exact model.
- The specific fault this record addresses: cannot make calls or send messages
What it does not cover
- ×The same symptom on a different Samsung product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
No usable service in the first place
What separates it No calls and no SMS, with the status bar showing no service or emergency only. Everything else on this page assumes service exists.
How to confirm Check the signal indicator and whether data works. Where there is no service at all, that is the problem to solve first.
- 2
The account is suspended or the line was ported
What separates it Emergency calls only on a phone that is otherwise perfect, often on a billing date. It looks identical to a hardware fault.
How to confirm Check the account status with the carrier before anything phone-side.
- 3
The number is blocked, or the phone is silencing unknown callers
What separates it Specific people cannot reach you, or calls go straight to voicemail without ringing. Both platforms offer silencing of unknown numbers, and block lists accumulate.
How to confirm Check the block list and any silence-unknown-callers setting. This produces a phone that appears to work perfectly and misses specific people.
- 4
Call forwarding was left on
What separates it Calls never arrive and go somewhere else entirely, often after a trip abroad or a voicemail setup. Forwarding survives until it is switched off.
How to confirm Check the call forwarding setting, which is easy to leave enabled and gives no indication that it is.
- 5
A focus mode silencing calls
What separates it Calls arrive but the phone does not ring, on a schedule. Focus and bedtime modes both do this deliberately.
How to confirm Check for an active focus mode and its allowed-callers list.
- 6
Wi-Fi calling on a poor Wi-Fi network
What separates it Calls fail or break up at home where cellular is fine, or the reverse. Wi-Fi calling prefers Wi-Fi even when the Wi-Fi is worse than the cellular signal.
How to confirm Turn Wi-Fi off and retry the same call. A clear difference identifies the path.
- 7
RCS or an internet messaging service rather than SMS
What separates it Messages fail to one person and work to everyone else, or fail on Wi-Fi and work on cellular. Modern messaging silently chooses between several transports.
How to confirm Send the same message as a plain SMS where the app allows it. Success there localises the fault to the internet transport rather than the network.
- 8
The recipient's number is stored in the wrong format
What separates it Messages fail to contacts saved without a country code, particularly after travelling or changing country.
How to confirm Compare a failing contact's stored number against the full international format.
- 9
A second line handling voice or messaging unexpectedly
What separates it Calls come in on one number and messages go out on another. Default lines for voice and messaging are separate settings.
How to confirm Check which line is the default for calls and which for messages.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- Whether calls fail, messages fail, or both — and whether it is to everyone or to specific people.
- The signal indicator and whether mobile data works, which establishes whether there is service at all.
- Whether it fails on Wi-Fi, on cellular, or both.
- Whether calls ring and are missed, or never arrive at all — those are different failures.
- Whether call forwarding, a block list, or a silence-unknown-callers setting is active.
- Whether the affected contacts are stored in full international format.
- The account status with the carrier.
Establish whether there is service at all
ReversibleNo service, or emergency calls only, makes everything else on this page irrelevant. 'Emergency calls only' in particular usually means the phone found a network and was refused by it, which is an account matter rather than a phone one.
Determine whether it is everyone or specific people
ReversibleEveryone points at service, the account or a system setting. Specific people points at a block list, a contact's stored number format, or the messaging transport. These share no further steps.
Check the block list and silence-unknown-callers
ReversibleBoth produce a phone that appears to work perfectly while specific people cannot reach you, and both accumulate quietly. Calls going straight to voicemail without ringing is the classic signature.
Check call forwarding
ReversibleForwarding left on after a trip abroad or a voicemail setup sends calls somewhere else indefinitely, with no indication on the phone that it is doing so. This is a five-second check that resolves an otherwise baffling symptom.
Turn Wi-Fi off and retry the same call
ReversibleWi-Fi calling prefers Wi-Fi even when the Wi-Fi is worse than the cellular signal available. Calls that fail at home and work elsewhere, or the reverse, are identified by this single test.
Send the same message as a plain SMS
ReversibleModern messaging chooses silently between RCS, an internet service and SMS. Success as plain SMS localises the fault to the internet transport, which is a completely different investigation from the cellular network.
Check the contact's stored number format
ReversibleA number saved without a country code fails in ways that look like a network fault, particularly after travelling or changing country. Comparing a failing contact against the full international format is quick and specific.
Check for an active focus mode
ReversibleCalls that arrive without the phone ringing, on a schedule, are a focus or bedtime mode with an allowed-callers list — not a call failure. The distinction matters because nothing about the network is involved.
Confirm which line handles calls and which handles messages
ReversibleDefault lines for voice and messaging are separate settings, and getting them crossed produces calls arriving on one number while messages leave from another. It is easy to set wrong and gives almost no indication.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- SM-S921*. Samsung Galaxy family; S Pen, foldable display, DeX, USB moisture and One UI features vary by exact model.
- Display
- 156.4mm (6.2" full rectangle) / 152.3mm (6.0" rounded corners), 2340 x 1080 (FHD+), Dynamic AMOLED 2X, up to 120 Hz. Samsung quotes two figures for screen size — the full rectangle and the rounded-corner measurement — which is why this phone is listed at two different sizes in different places and neither is wrong.
- Refresh rate
- Up to 120 Hz adaptive. A high refresh rate is one of the larger discretionary battery costs on this phone: it is genuinely smoother and it genuinely costs runtime, which is why battery complaints on this model are worth checking against the refresh-rate setting before anything else.
- Panel
- Dynamic AMOLED 2X. This is an AMOLED panel, so dark mode reduces consumption for real — black pixels are switched off rather than backlit — and a static bright element left on screen for very long periods is the one wear risk this panel type has.
- Rear cameras
- 50.0 MP + 10.0 MP + 12.0 MP. The main sensor is 50 megapixels, which produces substantially larger files than a 12-megapixel camera and is a meaningful contributor to how quickly storage fills.
- Zoom
- Optical Zoom 3x, Optical quality Zoom 2x (Enabled by Adaptive Pixel sensor). Zoom range is the practical difference between models in this line. A close-up that will not focus at the long end is normally the telephoto's minimum focus distance rather than a fault — taking the same shot at 1x confirms it in seconds.
- Video
- UHD 8K (7680 x 4320)@30fps. Resolution and frame rate dominate how quickly video fills storage and how hard the phone works thermally — sustained 8K recording is the single most common reason a Galaxy camera stops mid-take and warns about temperature.
- Memory and storage
- 8GB RAM with a 128GB storage tier. RAM matters directly to one symptom: apps reloading when you switch back to them is memory pressure rather than a crash, and it is more likely on the lower-RAM configurations.
- SIM
- SIM 1 + SIM 2 / SIM 1 + eSIM / Dual eSIM. Three combinations are supported, and the default line for calls, for messages and for cellular data are three separate settings — crossing them produces calls arriving on one number while data or messages use another, with almost no indication that anything is wrong.
- Wi-Fi
- 802.11a/b/g/n/ac/ax 2.4GHz+5GHz+6GHz, HE160, MIMO, 1024-QAM. This is Wi-Fi 6E hardware with 6 GHz support. A router running a newer standard falls back rather than refusing, so a difference against a newer phone on the same network is specification rather than fault.
- Bluetooth
- Bluetooth v5.3. Version affects range, reconnection behaviour and which accessory features are available — a newer accessory paired here operates at this version's capabilities rather than failing, which is regularly mistaken for a pairing fault.
- Connector
- USB Type-C. Note that a USB-C cable which fits is not necessarily rated for this phone's charging speed: USB-C carries several power profiles, and a data-oriented cable charges slowly or intermittently while seating perfectly.
- Processor
- 3.2GHz, 2.9GHz, 2.6GHz, 1.95GHz. Clock speed is not the useful number for troubleshooting; what matters is that sustained heavy work throttles, so performance measured while the phone is already hot is measuring the throttling rather than the phone.
- Samsung's own specification
- Samsung publishes the full specification for this model at samsung.com/uk/smartphones/galaxy-s24/specs/. Where any figure above matters to a decision, that page is the authority and this one is not.
- Biometric
- An in-display fingerprint reader, which looks through the screen. A thick or incompatible screen protector genuinely interferes with it, which is why unlock reliability often changes the day a protector is fitted rather than gradually.
- Modem
- 5G capable. In marginal 5G coverage the phone hands repeatedly between 5G and LTE, which costs more battery and generates more heat than settling on either — so the preferred-network setting is a real diagnostic lever rather than a preference.
- Charging
- Supports wireless charging. Coil alignment is tighter than it looks and a thick case, a metal plate or a card in the case defeats it entirely — so wireless charging failing while cable charging works is usually the case rather than the phone.
- Water resistance
- Rated water resistant, which is not waterproof and which degrades with age, drops and seal disturbance. The rating covers incidental exposure; it is not a guarantee, and moisture-detection warnings are deliberately conservative and can persist after the port feels dry.
- Platform
- Android, with a manufacturer interface layer over it. Battery optimisation and background-execution restrictions are applied per app and are far more aggressive than on iOS — which is why 'set this app to unrestricted' is a real fix here and has no equivalent elsewhere.
- Symptom boundary
- This record covers Samsung Galaxy S24 when it cannot make calls or send messages. A different symptom on the same hardware, or this symptom on a different Samsung product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !The account is suspended or the line has been ported away — a carrier matter that no phone-side change addresses.
- !There is no service at all and another phone on the same carrier works in the same place.
- !Calls connect and neither party can hear the other after the microphone and speaker have both been excluded.
- !Emergency calling itself is unreliable, which should be treated as urgent rather than troubleshooted at leisure.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. Samsung publishes this as "Galaxy phone is unable to make or receive calls". Samsung's article for a Galaxy phone that cannot place or receive calls, covering network, SIM, blocking and call-setting causes. Probed 2026-08-21: title-verified. What that article does not carry is the model boundary — it is written for a product line, and SM-S921* is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
What size is the Galaxy S24 screen?+
Samsung lists 156.4mm (6.2" full rectangle) / 152.3mm (6.0" rounded corners), at 2340 x 1080 (FHD+). The two size figures are the full rectangle and the rounded-corner measurement — both are Samsung's own numbers, which is why this phone appears at two different sizes in different places.
Does the Galaxy S24 have a 120Hz screen?+
Yes, up to 120 Hz adaptive on a Dynamic AMOLED 2X panel. It is worth knowing for battery complaints specifically: a high refresh rate is one of the larger discretionary costs on this phone, and it is the first setting to check when runtime is disappointing.
Does dark mode save battery on the Galaxy S24?+
Yes, genuinely — it uses an Dynamic AMOLED 2X panel, where black pixels are switched off rather than backlit. The saving is real though smaller than reducing brightness or refresh rate, which remain the larger levers.
What cameras does the Galaxy S24 have?+
50.0 MP + 10.0 MP + 12.0 MP, with optical zoom 3x, optical quality zoom 2x (enabled by adaptive pixel sensor).
How much storage and RAM does the Galaxy S24 have?+
8GB RAM and a 128GB storage tier. The RAM figure is the one that matters for a specific symptom: apps reloading from scratch when you switch back to them is memory pressure rather than crashing, and it is more likely on lower-RAM configurations.
Does the Galaxy S24 support eSIM?+
Yes — Samsung lists SIM 1 + SIM 2 / SIM 1 + eSIM / Dual eSIM. Because more than one line can be active, check which line is set as the default for calls, for messages and for cellular data separately; those are three settings and crossing them is easy to do and hard to notice.
What Wi-Fi does the Galaxy S24 support?+
802.11a/b/g/n/ac/ax 2.4GHz+5GHz+6GHz, HE160, MIMO, 1024-QAM. That is Wi-Fi 6E with 6 GHz support; a router on a newer standard falls back rather than refusing, so a gap against a newer phone is specification rather than a fault.
Can the Galaxy S24 record 8K video?+
Yes — UHD 8K (7680 x 4320)@30fps. Bear in mind that resolution and frame rate dominate both how fast storage fills and how hard the phone works thermally, and sustained 8K is the most common reason a Galaxy camera stops mid-recording with a temperature warning.
What Bluetooth version is the Galaxy S24?+
Bluetooth v5.3. Version affects range, reconnection and which accessory features are available — a newer accessory paired here runs at this version's capabilities rather than failing, which regularly gets misread as a pairing fault.
Calls go straight to voicemail without ringing.+
Check three things: call forwarding, the block list, and any silence-unknown-callers setting. All three produce exactly this, all three leave the phone looking perfectly healthy, and all three are easy to leave switched on without knowing.
Only one person cannot reach me.+
That rules out service, the account and the phone — all of which would affect everyone. What remains is a block list entry, that contact's stored number format, or the messaging transport being used for them specifically.
Messages fail to one contact and work to everyone else.+
Send the same message as a plain SMS if the app allows it. Modern messaging silently chooses between RCS, an internet service and SMS, and success as plain SMS localises the fault to the internet transport rather than the network. Also check that their number is stored in full international format.
Calls break up at home but are fine elsewhere.+
Turn Wi-Fi off and retry. Wi-Fi calling prefers Wi-Fi even when the Wi-Fi is worse than the cellular signal available, so a poor home network can produce worse calls than no Wi-Fi at all. One test identifies it.
My phone says emergency calls only.+
That usually means the phone found a network and was refused by it, which points at the account or the SIM rather than the radio. Check the account status with the carrier first — a suspended line and a failed radio look identical from the status bar.
Calls arrive but the phone does not ring.+
Check for an active focus mode and its allowed-callers list. Focus and bedtime modes silence calls deliberately and on a schedule, and nothing about the network or the call itself is involved.
I cannot call anyone after coming back from abroad.+
Check call forwarding first — it is commonly enabled while travelling and left on afterwards, and the phone gives no indication. Then check that the network selection has been returned to automatic rather than left on a manual foreign network.
Messages send on Wi-Fi but not on cellular.+
That points at the internet messaging transport rather than SMS. The two use completely different paths, and a transport that works on one connection and not the other is describing the network rather than the phone or the recipient.
Calls connect but nobody can hear me.+
That is a microphone problem rather than a calling one — and the first thing to check is whether a Bluetooth accessory is connected somewhere, because it takes the call's microphone with it. Record a voice note to test the microphone alone.
Does this answer apply to every Samsung model?+
No. It is scoped to SM-S921*. Samsung Galaxy family; S Pen, foldable display, DeX, USB moisture and One UI features vary by exact model.
What should I record before troubleshooting calls or messages?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing calls, messages. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Use another reliable path for urgent or emergency communication.
Answer for the exact device and software version shown above.