If you need to unlock your new or not-so-new iPhone 5 that is locked to AT&T, you have two options: call AT&T and ask them to unlock it or use a third party service like Keys2iPhone that sells iPhone unlocks. If you decide to go with option #1, be prepared to give AT&T your current phone number, name and other related information to verify your identity. You can call them directly at their customer support toll-free number: 1-800-331-0500.
At&t has repeatedly stated that as long as you meet their unlocking conditions, they will generate the unlocking code for your device. The conditions may be difficult to meet if you just bought a second hand iPhone from someone else, since they will need to verify that you are the original owner of the device before they can issue an unlock. Unfortunately, there are many unscrupulous sellers out there who can sell you a locked handset, or, even worse, a blacklisted iPhone in which case you can stop dreaming about getting it officially unlocked!
TIP: Always request the IMEI number of the iPhone you are about to buy and run it in the official Apple IMEI database to check if it has been reported stolen or blacklisted for some other reason.
For the reasons stated above it may be a real chore trying to get your iPhone 5 unlocked on your own. Naturally, the second option is to use a third party facilitating service that via their special relations with carriers secure official unlocks. There are many services out there – some are more expensive than others. Since you have already invested good money in purchasing your iPhone, it is only wise to pay a little more for a sure thing and avoid unpleasant surprises down the road. You can check customer reviews before ordering an unlock.
AT&T iPhone 5 comes in one version with a nano-SIM card slot for CDMA and GSM networks. The AT&T uses GSM technology and once they unlock your GSM slot, you will be able to use your iPhone with any GSM provider in U.S. and all over the world. The unlock will work with most European carriers that also use GSM technology. Simply check the world GSM coverage map for a list of GSM mobile carriers in your country.