Calls and messages on a Galaxy S21+ depend on the SIM, the carrier's network, VoLTE and Wi-Fi calling, and a few phone settings, and since the S21+ is a 5G phone from 2021, network changes by carriers are a common cause of trouble four years on. Start with the quick tests: switch Airplane mode on and off, restart the phone and look at the status bar for signal. In Settings, Connections, SIM manager, check that your line is on and set for calls, texts and data.
The checks in more detail
In Mobile networks, Network mode, choose the automatic setting that includes 5G, since a phone left on a single mode may lose signal when the carrier retires an older network. Carriers that have turned off 3G require VoLTE for calls to connect, so check that VoLTE and Wi-Fi calling are on, in the SIM settings or the Connections menu, depending on the carrier. For texts, check the messaging app and its settings. If you moved from an iPhone, iMessage may still hold your number; deregister it on the iPhone or through Apple's website so that texts arrive on the Samsung.
The Messages app uses RCS chat where the carrier supports it, and a fault with chat features can stop messages, so check Settings, Chat features and turn them off and on. Clear the Messages cache in Settings, Apps. For group texts, check MMS settings and the access point names for your carrier. Make sure that blocked numbers and spam filters are not catching the sender. SIM and software checks follow. Remove the SIM and look at it: a dirty or damaged SIM or one that does not match the phone's slot causes trouble, and an eSIM profile may need re-issuing by the carrier.
Test the SIM in another phone, or another SIM in the S21+. Update the software in Settings, Software update, since modem fixes arrive that way, and install the carrier's updates. Reset the mobile network settings through Settings, General management, Reset, if the problem persists, which clears saved networks. Ask the carrier to refresh the line and check that the phone is supported on the current network. If no signal is found with a good SIM, run Samsung Members diagnostics and contact Samsung with the serial number.
Differential
Likely causes of “Samsung Galaxy S21+ cannot make calls or send messages”, and how to tell them apart
- 1
A network mode that no longer fits
What separates it Calls fail when the carrier changes network
How to confirm Choose the automatic mode with 5G
- 2
VoLTE or Wi-Fi calling off
What separates it Calls will not connect
How to confirm Turn them on
- 3
iMessage holding the number
What separates it Texts from iPhones do not arrive
How to confirm Deregister iMessage
- 4
Chat features or MMS settings
What separates it Messages fail or are slow
How to confirm Toggle chat features and check MMS settings
- 5
A faulty SIM or eSIM
What separates it No service
How to confirm Test it in another phone or ask the carrier
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether calls, texts or both fail
- The network mode
- Whether VoLTE is on
- Whether the SIM works elsewhere
Try in this order
0 of 6 completedToggle Airplane mode
ReversibleAnd restart.
Check SIM manager
ReversibleAnd the network mode.
Turn on VoLTE and Wi-Fi calling
ReversibleIn Connections.
Deregister iMessage
ReversibleIf you left an iPhone.
Clear the Messages cache
ReversibleAnd check chat features.
Reset mobile network settings
ReversibleLast.
Model-specific
What is true of this model and not of its siblings
- 5G phone
- The S21+ supports 5G; keep the mode automatic.
- Carrier changes
- Older networks are retired over time.
Stop boundary
When this stops being a self-service repair
- !If no signal is found with a good SIM after a reset, contact Samsung with the serial number
- !If the line is the problem, contact the carrier
- !Back up before a reset
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why do calls fail on my S21+?+
VoLTE or the network mode may need changing.
Why do iPhone texts not arrive?+
iMessage may hold your number.
Will a reset erase my data?+
No, only network settings.
Can the carrier help?+
They can refresh the line.