Direct answer
A complete failure should be separated into power or eligibility, the external path, and the component itself before any reset. For iPhone cellular data, first test a call and public website in two locations with Wi-Fi off and VPN disabled.
What this covers
- iPhone cellular data with this exact failure state
- Diagnosis across carrier outage/account versus SIM/eSIM, coverage, VPN and per-app data settings
- Customer-accessible observation, settings and external components
What it does not cover
- ×A displayed manufacturer error code with a different documented meaning
- ×Live electrical, sealed-system, internal battery-cell or gas repair
- ×A claim that every model exposes identical controls
Capture the exact failure state
ReversibleRecord whether the feature is absent, disabled, powered but unresponsive, or showing a message. Expected behavior: attach to the carrier network and route allowed app traffic at the provisioned service level.
Isolate the component boundary
ReversibleTest a call and public website in two locations with Wi-Fi off and VPN disabled. Test the simplest supported configuration with unrelated accessories and optional services removed. Boundary to separate: carrier outage/account versus SIM/eSIM, coverage, VPN and per-app data settings.
Correct only the proven cause
ReversibleInstall carrier settings, correct the selected line/data permission or contact the carrier. Restore only the failed prerequisite or path; do not change working layers.
Verify and stop safely
ReversibleRepeat from a cold start and complete one normal use. Seek carrier or emergency support when service loss affects urgent calling.
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.
Exact questions
Common follow-ups
What should I check first when iPhone cellular data has this problem?+
Test a call and public website in two locations with Wi-Fi off and VPN disabled.
Why not factory-reset immediately?+
The useful boundary is carrier outage/account versus SIM/eSIM, coverage, VPN and per-app data settings. A reset can erase state without proving which side failed.
When should I stop troubleshooting?+
seek carrier or emergency support when service loss affects urgent calling.
Answer for the exact device and software version shown above.