Short answer: seeing "No SIM" or "SOS Only" after an iOS 27 update is usually fixable with a restart, a reseated card or an eSIM reactivation — not evidence of failed hardware.
Start by separating the two messages: "No SIM" means the system cannot read the card at all, while "SOS Only" means the card was read but the phone is not connected to its carrier's network. SOS Only also means another carrier's signal nearby is available for emergency calls — so it indicates the cellular connection is down, not that the device is finished.
Two messages, two different links in the chain
| What you see | What it means | Suspect first |
|---|---|---|
| No SIM / SIM not installed | The system cannot read the card | Tray seating, poor contact, oxidised contacts |
| SOS Only / No Service | Card read, but no carrier connection | Carrier activation, carrier settings, plan status, coverage |
| Stuck on "Searching" | Repeatedly trying to register | Coverage, Airplane Mode, carrier settings |
Locate your case in that table before working the order below. Mixing the two categories is the main reason this kind of troubleshooting drags on.
Universal first steps: restart and Airplane Mode
① Force restart once. Many "cannot read the card after an update" cases are just a wedged modem or carrier service process. Press Volume Up, press Volume Down, then hold the Side button until the Apple logo appears. The full sequence is in How to force restart a stuck iPhone.
② Toggle Airplane Mode. Turn it on for 15 seconds and off again, forcing the phone to re-register on the network. This is especially effective against a permanent "Searching".
Physical SIM: contact is everything
③ Reseat the tray. Eject it with the pin, check that the card sits flat and that the tray goes all the way back. You should feel it click home; if it is not fully seated, the card will not be read.
④ Wipe the card. Oxide and fingerprints on the metal contacts interfere with reading. Wipe them with a dry cloth or a soft eraser — no liquid, and do not bend the card.
⑤ Cross-check in another phone. Put the card in another phone:
- it works there → the card and carrier are fine, the problem is your phone, so continue below;
- it does not work there either → the card or carrier is the problem, so contact the carrier and stop fiddling with the phone.
This is the highest-value single step in the whole list, because it eliminates half the possibilities at once.
eSIM: activation is everything
An eSIM cannot be reseated, so the issue is usually that the profile needs to be re-pushed:
- Check whether it is disabled —
Settings → Cellular, and see whether that line was turned off or set to data-only; - Reactivate it — most carriers offer a re-push flow in their app or on their site, and support can also send the profile again. One fresh activation after a system update is a normal, common action;
- Confirm the plan status — unpaid bills, suspended lines and expired identity verification all show up as "No Service" and have nothing to do with the phone;
- Do not delete the eSIM profile on your own. Until you have a fresh activation code in hand, deleting it can remove your way back. Confirm the carrier can re-push it first.
Carrier settings and coverage
⑥ Update carrier settings. When one is available, Settings → General → About shows a prompt — just confirm it. These settings carry carrier-side parameters and occasionally need to resync after an update.
⑦ Rule out coverage and physical factors. Move somewhere else (deep indoors, lifts and underground car parks are naturally poor); check that there is no carrier outage in your area; confirm no metal case is sitting over the antenna area.
When it is genuinely a problem
- Another phone's card also cannot be read, and repeated restarts do not help — that points at the SIM reader or the modem, and is worth an Apple check;
- the card works in another phone but never in yours, with clean contacts and a fully seated tray — likewise a phone-side hardware issue;
- no service only in a particular place, fine elsewhere — a coverage issue, unrelated to the phone and the update;
- it comes with a clearly hot body or a sudden jump in drain — background post-update work may still be running; see iOS 27 battery drain after update.
One practical point to close on: No SIM and SOS Only are usually not "the update broke my phone" — they are "the link between the card and the network was never established". Restart, reseat or reactivate, then cross-check. Do not rush into replacing the phone over one message.