Why does my phone say No SIM or SIM not supported?
Four causes: a tray or contact problem, a failed SIM, a network-locked handset, or a SIM the network has deactivated. Two swap tests separate them in five minutes.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 4 min
- Safety
- caution
Short answer
Restart the phone first — a stuck registration produces this and clears on restart. Then eject the tray, check the SIM is seated the right way round and the gold contacts are clean, and reseat it. If it persists, put your SIM in another phone and another SIM in yours: if your SIM works elsewhere, the phone is at fault; if it fails everywhere, ask the network for a replacement. Not supported specifically usually means the handset is network-locked.
The two messages mean different things and it is worth reading yours carefully. No SIM means the phone cannot see a card at all. SIM not supported, invalid SIM, or SIM locked means the phone can see it and is refusing it — usually because the handset is locked to a different network, which is a completely different problem with a completely different fix.
Safety
Step by step
- Restart the phone before anything physical.A failed registration or a stuck modem state produces a No SIM message with a perfectly good SIM in place. A restart resolves a meaningful share of cases and costs thirty seconds. Toggling aeroplane mode is a quicker version of the same idea.
- Eject and inspect the tray.Use the ejector pin in the small hole beside the tray — a straightened paperclip works. Check the SIM is the right way round, sitting flat in its recess, and that the tray goes back in fully and flush. A tray not quite home is a very common cause after travel or a case change.
- Clean the contacts.Wipe the gold contacts on the SIM with a dry lint-free cloth. Do not use liquid, and do not touch the contacts with your fingers more than necessary. Look into the slot with a torch for lint or a bent contact pin, which happens when a SIM has been inserted the wrong way round.
- Do the two swap tests.Your SIM in a different phone, and a different SIM in your phone. This is the whole diagnosis. Your SIM failing in both means the SIM or the account. Your SIM working elsewhere while another SIM also fails in your phone means the phone's SIM reader.
- Check the account if the SIM fails everywhere.A SIM is deactivated the moment a replacement or an eSIM is issued for the same number, and networks also deactivate SIMs on unpaid accounts and on pay-as-you-go numbers unused for a long period. Log into the network account over wi-fi, or ring them from another phone.
- Read a 'not supported' message as a network lock.If the phone accepts one network's SIM and refuses another's, it is locked. Handsets sold on contract or on pay-as-you-go may be locked, though UK networks now generally unlock free on request and many sell unlocked as standard. The network that sold the handset is the one that unlocks it.
- Rule out a physical event.A drop can unseat the SIM reader's connector; water can corrode it. If the message began immediately after either, the swap tests will point at the phone and a repair shop is the next step rather than more settings.
- Try a network settings reset before giving up on the phone.Occasionally a corrupted mobile configuration produces this. Resetting network settings clears wi-fi passwords and pairings but rebuilds the mobile configuration from scratch. Worth doing before concluding the reader has failed.
If it doesn't work
Comes and goes, especially when the phone is moved or in a pocket
Cause: The tray is not fully seated, or the reader's spring contacts have weakened — Fix: Reseat the tray firmly. If it recurs, a thin strip of paper folded behind the SIM is a widely used temporary bodge that works — but it is a sign the reader needs attention, and it is a reason to consider moving the line to an eSIM if the phone supports one.
Started after inserting a SIM from another country
Cause: A network lock, or a SIM of the wrong physical size in an adapter — Fix: Check the lock status with the original network. SIM adapters are a genuine hazard — a badly fitting adapter can jam in the reader and require a repair to remove.
Phone works on wi-fi but shows no SIM permanently
Cause: SIM deactivated, or the reader has failed — Fix: Do the swap tests. If the phone is otherwise good and the reader has failed, ask the network whether they can supply the line as an eSIM instead — on a phone that supports it, that bypasses the failed hardware completely and is often the cheapest fix available.
Emergency calls only
Cause: The phone sees a SIM but cannot register on the network — Fix: Restart, check for an outage, and check the account is in good standing. If it persists in a known-good coverage area with a known-good SIM, it is the phone.
Questions people ask
Can I use the phone without a SIM at all?
Yes, over wi-fi, for everything except calls and texts on your number. That is exactly how a spare phone becomes a music player, a camera or a child's device, and it is worth remembering while you wait for a replacement SIM.
How do I know if my phone is network-locked?
Put another network's SIM in it. If it works, it is unlocked. There is no reliable way to tell from settings alone, and third-party check services are unnecessary — the swap test is definitive and free.
Does it cost anything to get a phone unlocked?
In the UK, networks unlock handsets they sold, free, on request, once any contract conditions are met. Paying a third party is unnecessary and some of those services are fraudulent.
Is an eSIM immune to this?
It removes the tray, the contacts and the reader from the equation, so the physical failure modes go away. Profile and account problems can still leave you with no service, and they are harder to diagnose with a swap test.