I'm on AT&T and have a question regarding family members' phones that have just received unlock approvals from AT&T. My family members bought their phones from AT&T, so they are locked to that carrier. Since the unlocks have been approved, I know I can just pop in a different SIM to finalize the unlock. If I'm not mistaken, this can be any SIM card, even if it's not active or from a different country, right? I have inactive ones from U.S. and foreign carriers alike that would be easy to use. I have active ones on Sprint but that's a little harder, as I have to contact Sprint to program the SIM's ICCID to the phone's IMEI. How can I know when the unlock has worked if using an old and inactive SIM? Does the carrier name text in the top left read "No Service" instead of "Invalid SIM"? Lastly, does this have to be done in the U.S. to work? Or if they travel abroad, buy a local SIM, and then insert it into the phone, will that also work? I'm not sure if one has to be in AT&T coverage territory to finalize the unlock on an AT&T phone, for example. Thanks for your help!