Unlocking your AT&T phone has never been easier due to the recent law passed on February 11th 2015. This newly adopted law makes it a requirement for any carrier to unlock phones from customers who request an unlock.
AT&T Customers - If you are in good standing and the device was activated with a service commitment or installment plan, AT&T will unlock your device if the phone/account has been active for at least 60 days with no past due or unpaid balance. In this case, you can either fill out an unlock request through their website and you will be contacted within 24 hours, or you can contact AT&T's customer service directly and notify the representative that you would like to unlock your device. Once you have made the request, the phone should become unlocked within the next 48 business hours. At that time, you should have no problem switching your phone to a compatible carrier.
Non AT&T Customers - If you have obtained an AT&T from a 3rd party like Craigslist or Ebay, you'll need to unlock the phone before you can use it with another carrier. Because you do not have an account or any affiliation with AT&T, they may oppose your request to have the phone unlocked. If this turns out to be the case, you still have a another option to have the device unlocked. What you can do is navigate to Craigslist where there are usually quite a few local organizations who will unlock smartphones. The cost of this service ranges from $20-$50 and takes roughly 48 business hours. We do want to add to use caution if deciding to take this approach as the companies are less regulated.