Activation question

[RRDave]

Got a question about the activation process. Yesterday I exchanged a dead 3GS at the Apple store under warranty. I do not have a contract with AT&T. Before they would exchange it, the Genius said that it had to be activated with an AT&T sim. I borrowed a friends sim from his 3GS (on AT&T) and all seemed to go OK. I got the replacement phone (now activated) and put the sim back in my friends phone and all seems to be good. What is the downside to this and can anything go bad long term?

[eyeRobot]

Nothing bad. You're sorted.

You may need to borrow your friends card again if your phone ever gets restored.