this is a stolen iphone isnt it connect to itunes, and press the top right button at the top and the button on the screen at the same time while connected to itunes, and a step by step process should appear on itunes
put a at&t sim card in the phone, and call up at&t and tell them you are leaving the country if they can unlock the phone for you, and when that is done, try puttin the t-moible sim card in.
Just use blackra1n... and then blacksn0w... its really easy its all one click. But remember T-Mobile Uses different 3G bands so it wont work on the iphone You will only be able to use EDGE