An active SIM is recognised by the provider and authorised to use the account. That does not necessarily mean it has credit, a current bundle, good coverage or working mobile data. Test each part separately.
Start with the provider account
Sign in to the official app or account page over Wi-Fi and check:
- the telephone number is listed;
- the account is open and not suspended;
- the correct SIM or eSIM is attached;
- there is an active plan, credit or allowance where required;
- no replacement SIM or number port is still pending.
Check what the phone can see
Open SIM or mobile-service settings. A physical SIM should appear as a line or network entry. An eSIM should appear as a downloaded profile. If the line is missing entirely, investigate detection or installation rather than account activity.
Test ordinary service
- Check that the line is enabled and network selection is automatic.
- Make an ordinary call to a trusted number.
- Ask that person to call back.
- Send and receive an SMS if the plan includes it.
- Turn Wi-Fi off and test mobile data.
Do not call 999 or 112 as a test. A phone may display emergency-service wording even when the SIM is inactive.
New or replacement SIM
Follow the provider's activation instructions and stated waiting time. A SIM swap may deactivate the old card before the replacement begins working. If the stated period has passed, ask the provider which SIM serial or eSIM profile is attached to the number.
PAYG SIM
A PAYG SIM may remain registered while having no usable credit or bundle. It can also be disconnected after prolonged inactivity. Check the current provider rule rather than assuming that receiving a text or seeing signal resets the inactivity period.
Test in another phone only when safe
A physical SIM that works in another compatible unlocked handset is probably active, but the test may expose messages or account access on that device. Do not use a borrowed phone unless the owner agrees and you can remove your account traces afterwards.
When to contact the provider
Contact the network if the account says active but the line cannot register, the SIM is not provisioned, a port is delayed, a replacement is pending or the provider has disconnected a PAYG number.
The evidence worth recording
Separate card detection from service activation. A phone can display the network name while outgoing use is barred, and an account can be active while the card itself is damaged. Check the provider account, then test an ordinary outgoing call, an incoming call, SMS in both directions and a small mobile-data task.
- Record any exact error message.
- Check balance or allowance for PAYG.
- Confirm that a recent replacement or port has completed on the provider's system.
Official information checked
Information checked on 25 July 2026. Activation and inactivity rules vary by provider and plan.
