If you buy an iPhone from AT&T, it will be 'locked' to AT&T's network. That means if you try to put in a T-Mobile SIM, it won't work. Same with an international SIM if you're traveling. How To Unlock A Sprint Cell Phone For Free.
Summary: There are three methods available to unlock your iPhone 6/6s, or 6 plus/6s plus – software unlocking, hardware unlocking, and IMEI unlocking. Don't feel trapped by AT&T — unlock your iPhone and enjoy your freedom!
Just because you're locked, though, doesn't mean you can't unlock. AT&T has a process in place for you to request a code to do just that.
Of course, there are requirements and some restrictions you needed to be aware of first. • • What requirements does AT&T have for unlocking? Before requesting an unlock code from AT&T, there are some requirements you'll need to know. • The phone must be locked to AT&T (of course). • It can't be reported as lost or stolen (also, of course). Free Unlock Codes For Android Phones. • It can't be associated with fraudulent or illegal activity (see where we're going here?). • All of your iPhone's service commitments and installment plans are completed, and all early termination fees are paid in full.