swapping sim cards between two iphone 3gs?

[luckyduckyy]

I have an Iphone 3g with AT&T contract, data plan etc. My phone is pretty beat up and I have been thinking about replacing it, but dont want to pay the 500 or whatever it costs to get a new one without a new contract. A friend of mine has a brand new Iphone 3g he bought online but never activated. I don’t think it is unlocked or anything—I’m pretty sure he just ordered the phone off ATT.com and never activated it because he ended up going with a blackberry. My question is, if I just buy this phone off of him to replace mine, can I just pop my current sim card into it and keep my same #/data plan etc. Will it work right away, or would I need to do something in Itunes for it to work?
Thanks

[dvdhsu]

I have an Iphone 3g with AT&T contract, data plan etc. My phone is pretty beat up and I have been thinking about replacing it, but dont want to pay the 500 or whatever it costs to get a new one without a new contract. A friend of mine has a brand new Iphone 3g he bought online but never activated. I don’t think it is unlocked or anything—I’m pretty sure he just ordered the phone off ATT.com and never activated it because he ended up going with a blackberry. My question is, if I just buy this phone off of him to replace mine, can I just pop my current sim card into it and keep my same #/data plan etc. Will it work right away, or would I need to do something in Itunes for it to work?
Thanks

It should work perfectly.
You might need to call AT&T up and tell them the IMEI number, and tell Apple the serial number though.