What's going on

When a phone functions seamlessly on Wi-Fi but refuses to make regular calls, send SMS, or load mobile data, the device's cellular subsystem is offline. Your phone relies on separate hardware antennas and software stacks for Wi-Fi and mobile networks. When Wi-Fi works, the CPU, main board, and display are functioning fine, but the cellular modem or signal path is failing to connect to cell towers.

This issue can manifest suddenly after a software update, a hard drop, water exposure, or an unexpected carrier network configuration change. Dissecting whether the root cause is soft (APN, SIM, account) or hard (board-level baseband or disconnected antenna flex) will save you unnecessary repair costs.

Symptoms people notice

• The top status bar reads No Service, Searching, or Invalid SIM when Wi-Fi is disconnected.
• Messaging apps like WhatsApp or iMessage work over Wi-Fi, but standard green-bubble SMS texts immediately fail.
• You can make calls only when Wi-Fi Calling is toggled on in settings.
• Cellular Data switches in settings appear greyed out or flip back off automatically.
• An alert appears on startup warning that an update is required to use cellular features on this phone.

Likely causes

1. Network Configuration Glitch: Corrupted network cache or an outdated carrier bundle blocking tower registration.
2. SIM Card Issues: De-prioritized, damaged, or dirty physical SIM card, or an unassigned/corrupted eSIM profile.
3. Carrier Account or IMEI Hold: A billing issue, roaming lock, or reported device flag at the carrier level.
4. Incorrect APN Settings: Common with budget or prepaid carriers (MVNOs) where cellular data settings must be manually configured.
5. Hardware Antenna Disconnection: A physical impact causing the internal coaxial antenna cable to pop off its logic board terminal.
6. Baseband IC Failure: Physical or liquid damage affecting the baseband modem chip on the main circuit board.

Quick checks first

Before opening up hardware or buying replacement parts, rule out basic software and carrier issues:

• Test a second SIM: Borrow a known working SIM card from another phone on the same network to test your SIM slot.
• Verify Roaming and Data Toggles: Ensure Mobile Data and Data Roaming (if traveling) are toggled ON in your Settings app.
• Check for Carrier Updates: While on Wi-Fi, go to your phone's About menu to trigger any pending network profile updates.
• Review Network Coverage: Cross-check with a friend on the same carrier to ensure you aren't in a localized coverage dead zone.

For broader software troubleshooting routines, review our comprehensive DIY repair guides for mobile devices.

When it's a real repair

If resetting network settings and swapping the SIM card yields no results—or if your device explicitly throws a hardware cellular error—you are dealing with a physical issue.

Drop damage frequently knocks loose the small, delicate coaxial antenna cables that run along the side frame of modern smartphones. If the device was recently opened for a battery or screen replacement, an antenna cable may have been pinched or left disconnected entirely.

More severe drops or water exposure can crack the solder joints under the baseband Power Management IC (PMIC) or baseband processor, preventing the phone from communicating with its cellular radios altogether.

DIY vs professional repair

Replacing a physical SIM tray, re-seating a popped antenna cable, or replacing an accessible charge port/antenna daughterboard are manageable DIY tasks if you have precise tools (prying spudgers, precision screwdrivers) and follow a teardown guide. Check our common problems guide to see how simple component access is on your specific model.

However, if the failure is linked to the logic board—such as a torn trace or a fractured baseband chip—micro-soldering equipment and specialized diagnostics are required. If you prefer to avoid micro-soldering or risk tearing delicate internal ribbon cables, consulting a mail-in repair service or an LML Repair Expert is recommended.

Next steps

1. Call your carrier: Confirm your device IMEI is clear and your line is fully provisioned for 4G/5G data.
2. Backup your phone: Perform a full backup to the cloud or a computer while connected to Wi-Fi.
3. Inspect the hardware: If you have hardware experience, follow one of our detailed repair guides to open the device and inspect all cellular flex connections.
4. Get technician support: If board-level solder work is needed, submit your device details to a professional technician for advanced repair options.