answer:I have an unlocked phone and am an AT&T customer. I purchased my phone directly from the company that manufactured it (which for you would be Google) and then went into an AT&T store to get a SIM card to fit it, because the phone required a micro SIM card and my previous phone had the older larger version. My understanding is that if my former SIM card had fit, I would have simply been able to put it into my unlocked device—I did this exact thing many years ago with another unlocked device. I think the SIM card needs to be from the phone company directly, though I might be mistaken (someone can verify or correct that). I believe AT&T provided the SIM card for no charge, so there was little incentive to purchase one on my own…. Yeah, free SIM card and no annual contract… more information as you scroll down the page… unless you know something about SIM cards that I don’t! (Which is very probably, as I don’t know very much.) From what I understand, you can also purchase phones from AT&T, and once you pay for the phone full AT&T will help you unlock the phone. This might be at the end of the payment schedule (which I guess is now 30 months), or earlier if you pay it in full earlier. Basically, you need to pay for the phone in full to have it unlocked. Hope that helped!