To unlock your iPhone from its carrier, you'll likely need to contact your carrier directly to cancel your contract.

If you need to find out your iPhone's carrier without a SIM card installed, you can do so through the Settings app.

A user has an iPhone 3G from a relative in France. Has the phone, but no SIM card. Can't activate it initially because he has T-Mobile, so no valid SIM at all. I can't even use an ATT SIM (in US) so ...

Many times it happens that there is no network in the SIM. There is no WiFi or data either and if you have to call someone, it becomes a problem. In such a situation, you do not understand how to call ...