If SMS has stopped working on your phone — messages won't send, OTPs don't arrive, or you keep getting "not activated on this device" errors — the fix is almost always simpler than it looks. This guide walks through every layer (device, carrier, account) you need to check.
The 30-second fix to try first
- Toggle airplane mode. Turn it on, wait 10 seconds, turn it off. This forces your phone to re-register with the carrier and fixes most SMS issues caused by tower hand-offs.
- Restart the phone. Full reboot — not just screen-off. This clears any stuck cellular state.
- Send an SMS to yourself.If it arrives within 30 seconds, SMS is working. If it doesn't, proceed to the deeper checks below.
Device-level checks
iPhone
- Settings → Messages → Send & Receive:ensure your phone number (not just email) is checked under "You can be reached".
- Settings → Messages → iMessage:if iMessage is on but your SMS isn't going through, toggle it off for a minute then back on. iMessage sometimes intercepts what should be a normal SMS.
- Settings → Cellular → SIM: confirm your SIM is enabled and has the right label (primary line).
- Settings → Cellular → Cellular Data Options → Voice & Data:make sure it's set to 5G, LTE, or 4G. Some carriers (Vi especially) drop SMS when the phone falls back to 2G.
Android
- Settings → Apps → Messages → Permissions: SMS permission must be granted. Required on Android 12+ after certain updates.
- Settings → Apps → Messages → Set as default app: if you switched to WhatsApp or another messenger as your default, SMS may be disabled.
- Settings → Mobile Network → SIM: confirm the SIM is enabled and check the APN settingsmatch your carrier's defaults (each operator has specific APN values on their website).
- Messages app → Settings → Advanced → Message Centre: this is the SMSC number and it must match your carrier. Wrong SMSC is the #1 Android SMS issue.
Correct SMSC numbers for Indian carriers
If your SMSC is wrong, outgoing SMS fails silently or gets stuck at "sending". Here are the current defaults:
| Carrier | Default SMSC number |
|---|---|
| Jio | +917010075099 |
| Airtel | +919895051914 |
| Vodafone Idea (Vi) | +919821099999 |
| BSNL | +919434099999 |
| MTNL Delhi | +919868001111 |
Carrier-level issues
If device settings are correct and SMSstill doesn't work, the issue is probably on the carrier side.
New SIM not activated
When you insert a new SIM, activation can take 4–24 hours. During that window, voice and data might work but SMS doesn't. If you're past 24 hours, call your carrier's activation helpline:
- Jio: 199 (from the Jio SIM) or 18008899999
- Airtel: 121 or 18001034444
- Vi: 199 or 19826200000
- BSNL: 1503
Postpaid overage or unpaid bill
On postpaid, some carriers block outbound SMS (but not incoming) when you're past due. Check your balance in the carrier app or pay the outstanding amount.
Prepaid balance insufficient
If your plan doesn't include free SMS and your main balance is zero, outbound SMS will fail. Top up or upgrade to a plan with SMS included.
International roaming
When you're roaming internationally, outbound SMS costs ₹3–20 per message depending on the destination. If roaming SMS isn't enabled on your account, it silently fails. Enable "International SMS" in your carrier's app.
When OTPs specifically aren't arriving
If your SIM works for regular SMS but OTPsfrom specific services don't arrive, the issue is upstream. Check in order:
- Is the service's SMS provider having an outage?Some providers experience partial delivery failures with specific carriers. Check the service's status page.
- Is your number on DND with a strict setting?
START 0on DND only blocks promotional, not transactional — but if you accidentally enabled a setting that filters transactional too, OTPs stop arriving. Check with your carrier's DND helpline (1909). - Have you blocked the sender? If you previously reported the service as spam, your phone may be filtering them. Check your blocked list.
- Is your phone's SMS storage full? Rare but happens — some phones silently drop new SMS when storage is full. Delete old threads.
- Is the phone number on file with the service still correct? If you ported to a new number (MNP), the service might still be sending to your old number.
If you're the business sending the OTP
When customers report "not receiving your OTP", the issue is almost always one of these on your side:
- Template or header suspendedat the DLT layer. Check your SMSLocal dashboard for delivery failures tagged "Header rejected" or "Template mismatch".
- Customer is on DND with strict filtering. Make sure your header is correctly categorised as transactional.
- Rate-limiting on carrier side. Sending 50 OTPs to the same number in 5 minutes triggers carrier-level abuse protection.
- International format issues. Indian numbers should be stored as
+91XXXXXXXXXX, not0XXXXXXXXXXor plain 10-digit.
FAQ
Half the "SMS broken" tickets we see are solved by airplane-mode toggle. The other half are SMSC mismatches or a stuck iMessage number. Almost none are ever carrier outages.
