Seeing “Not Delivered” under your texts is one of the most annoying iPhone problems. SMS is the fallback channel — it rides on your cellular network, not the internet — so when texts won’t send, the cause is usually something simple: a signal hiccup, a wrong setting, or a carrier-side issue. Here’s how to find it and fix it.
Quick checks that fix most cases
- Check your signal. SMS needs cellular service. If you see “No Service” or a single bar, texts may fail. Turn airplane mode on for ten seconds, then off, to force the phone to reconnect to the nearest tower.
- Restart your iPhone. A quick restart clears temporary radio and messaging glitches. Hold the side button and either volume button, slide to power off, wait a few seconds, then power it back on.
- Turn on “Send as SMS”. Go to Settings → Messages and make sure Send as SMS is enabled. Without it, your phone won’t fall back to regular texting when iMessage is unavailable. Also confirm iMessage itself is switched on.
- Verify the number and check blocked contacts. Make sure you’re texting a valid number with the right country code, then look in Settings → Messages → Blocked Contacts — if the recipient is on the list, your texts won’t go through. (If the problem is specific to one contact on Android, see our guide on iPhone not receiving SMS from Android.)
- Check the date and time. Go to Settings → General → Date & Time and enable Set Automatically. A wrong clock can quietly break message delivery.
- Update carrier settings. Go to Settings → General → About. If a carrier-settings update is available you’ll get a prompt — accept it. These updates fix known network bugs.
- Toggle iMessage off and on. In Settings → Messages, switch iMessage off, wait thirty seconds, and switch it back on. This re-registers your number with Apple’s messaging servers. Apple’s guide to troubleshooting messages walks through the same checks.
If it still doesn’t work
- Reset network settings. Go to Settings → General → Transfer or Reset iPhone → Reset → Reset Network Settings. This clears Wi-Fi passwords and cellular settings, so keep your passwords handy. It often fixes stubborn send failures.
- Reseat your SIM or check your eSIM. Remove and reinsert a physical SIM, or in Settings → Cellular verify your eSIM line is active. A loose or deactivated SIM is a classic cause of SMS failures.
- Call your carrier. If texts fail for every contact, the problem may be on the carrier side — a plan issue, an outage, or SMS blocked on your account. Only they can check that.
- Back up and get help. As a last resort, back up your iPhone and contact Apple Support. (And if messages vanished instead of failing to send, our guide to recovering deleted messages on iPhone may help — plus how to fix SMS not arriving on your Mac.)
Frequently asked questions
Why does iMessage work but SMS fails?
They travel different routes. iMessage goes over the internet (Wi-Fi or mobile data); SMS goes over the cellular voice network. So iMessage can work fine while SMS fails if your cellular signal or carrier SMS service has a problem — check Send as SMS and your signal first.
Do SMS messages cost money?
It depends on your carrier plan. Many plans include unlimited SMS, but some charge per message, especially international texts. If you’re being charged unexpectedly, check your plan details or ask your carrier.
Conclusion
Most SMS failures come down to signal, settings, or the carrier — and the steps above resolve the vast majority of them in a few minutes. Work through the quick checks first, reset network settings if needed, and call your carrier if nothing helps. For a visual walkthrough, this video guide demonstrates the same fixes step by step.
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