Hi i just bought an iphone from a guy. Iphone 8gb firmware 1.1.1 serial 7s726 baseband 3.9

Now the guy used this phone with at&t also it is jail broken because it has an installer in it. so the guy told me that ill be able to use it with t-mobile just install anysim 1.1 and then ill work. so i tried that and no luck also he said that he called at&t so they can release the phone ???? no idea whats that mean.

any ways i wanna use this phone with t-mobile so is it posible since the phone was used with at&t. if so how ? thanks alot