I really screwed up last week and purchased a GSM phone from Ebay. Big, big mistake. The phone is a new unlocked Samsung Galaxy S III GT-I9300 (Model # SGH-T999) with Android Version 4.1.1 ”Jelly Bean”. When it arrived, the phone had "T-Mobile" written on the back and all the apps seem to be from T-Mobile. It also states that the carrier is T-Mobile. The seller of this phone never reviled this information. However, it is a very nice phone. Here is my problem. I am using H20 Mobile prepaid service which exclusively uses AT&T Mobile. I want to use this phone for AT&T service because they have the best reception in my local area. The T-Mobile reception is terrible here. While driving, sometimes the phone wants to connect to T-Mobile towers and indicates the service is not available. Also, the internet connection tries to connect through T-Mobile while on the road. The message says I don’t have an account. My question: is there software available for download that I can reprogram this phone and use it with AT&T service?? I want to completely wipe T-Mobile off this phone. I am not sure what the next step should be but I have downloaded the latest ROM software "51c37773dec1b" V 13 called ”Jelly Bean”. I haven't installed it on my phone yet. Is it possible that this software upgrade might resolve the problem of this phone trying to connect to T Mobile towers???