I am new to ATT Wireless and so far I love it. I do have a question about the ability to buy a phone from a different source and use it on thier network.

I was searching the web and saw a zillion places where I could buy an unlocked phone that supports the GSM bands ATT uses. Would I just be able to pop in my ATT sim and it would work?

Would I lose any functionality?

Do I need to call ATT and give them the IMEID number. I ask because when I activated my service I had to.

Please get me up to speed on this. Thanks