I'm going to show you how to get AT&T to unlock your iPhone, and this is an official unlock, no jailbreak is needed. Make sure to go get your IMEI number from your iPhone.
This is my AT&T iPhone 5s running iOS 8.1.2, you can see here it says ATT and iOS, and I'm going to try to unlock my iPhone, I purchased this, I am factory unlocked off of eBay, you can also because it's an AT&T phone, you could try to request an unlock off AT&T's website, I don't have AT&T services, it's kind of difficult, other people say they can do it very easily, I haven't had too much success, so again I just purchased a cheap one dollar unlock, it might last, it might not, but there's just sort testing purposes and so over here are the instructions that I was given.
It says open iTunes, I'm sure there's no SIM or any GSM SIM card, usually they say any GSM SIM card, that's not AT&T, but this one says put in the original SIM, connect your phone to a computer, and then do backup in the store, and then it should say that it's unlocked, in this case, I believe in anything that's iOS 7, and above all, you have to do is put in a new SIM card that's not for the same carrier, so here's my t-mobile SIM card, which I'm going to put into this phone, so they sent me an email saying I could go ahead and do it, so here I am inserting it, that activation required I have Wi-Fi connectivity, so I'm just going to try to unlock the Wi-Fi, so that's it, could take a few minutes, I think it was running it iOS 6, I'm not sure what the basis, but I wish Apple would tell you, I'm recording off, see over here, it says t-mobile, then you see if I can turn down the brightness, see is this t-mobile 18-point, so it's unlocked, so you can just do them Wi-Fi.
I have another crappy post that I made, but you don't have to a backup and restore your phone necessarily, it's only if you get stuck, so there you go, it says no service right now because I don't have an active SIM, but that's it.