I've been a ST user for almost 3yrs, love it. It was my first and only prepaid experience (I've had TM and Verizon, ect before). I was thrilled once they finally started offering the ability to use Android Smartphones as when I originally switched I had to leave my smartphone behind for a very limited phone! Now I have a couple of questions as I'm looking for a new phone upgrade and don't want any that ST currently has to offer. Since I'm already a ST user. If I purchase an unlocked phone can I use my current ST sim card in my new phone instead of purchasing the ATT sim from their site? Also if I purchase an ATT phone could I do the same (my current ST service is through ATT) and use it with ST. If I have to get a new sim $15 is no big deal, but if I don't need it then obviously no reason to bother.