I got an iphone 4 from a friend as a gift and he only gave me the phone and sim card, and i tryed my friends iphone 4 sim card, as it is the same carrier (bell) and it said no service, im wandering if you can only use a sim card one iphone 4 cause of the activation? cause im worried if he got me a black listed iphone 4.. anyone help?

my bad, it showed 1 bar first then it said no service***

Your best option is to contact the carrier and explain situation to them. They can lookup to see if phone is blacklisted etc.

i have the same question