okay I currently have an iPhone 3gs but the ios is still 3.1 and I want to update it to the latest version 6.1 but I'm not sure if it will work with t-mobile because I heard that it will make it locked or something. I can't download any apps that have an ios of 3.2 or higher. I really want to update it but I'm afraid to mess it up or unlock it. can I update the ios using a t-mobile sim or will it mess up? I really need further information please and thank you sooo much 