Hello i just got an iphone from someone on ebay it has 1.1.1. but im not sure if they updated it to 1.1.1 from 1.0.2 i think they used it already with at&t i want to unlock it to use it with my T-mobile but im not sure where to start because its not new out of the box like the guide says

also how can i find out if the phone is unlocked already when i put my t-mobile sim in it it tells me incorect sim card but the at&t sim it doesnt say anything just no service someone please help