I was given an Iphone4 from lost and found from this summer as it was unclaimed. I have found that the carrier was "three" out of Europe, and I need to change it to ATT. I have the Sim Card cutter but can not seem to figure out what exzactly I need to do to get this to work. Im on 4.3.5 right now as well. Please help or guide me to somthing I can understand step by step so that I can start using this I4 instead of my I3. Any ideas or help really is appreciated. I have been trying to do this myself from youtube videos but have had no luck.