My dad bought my son a iPhone 4s for his xmas we stuck his Tmobile sim in all appeared to be working fine. I was changing over my sons contract from tmobile to 3 over the festive period and the number change over went through today. Put the 3 sim in the phone but I keep getting a sim is not supported or similar type error when trying to activate. Now I may have wrongly assumed the phone was sim free but my dad would have no idea what network my son was on and I am pretty sure T mobile don't sell payg iPhone 4's. Parents on holiday so I can't get in touch with them to find out where he got it. I assume the phone is now locked to T Mobile ?