3GS and 3G....can you swap sims? Are they compatiable?

[MatrixPrime]

Pretty much what the title asks. Let me set this up. I have a 3G, and I'm not eligible for the discounted upgrade, so I would have to pay full price to upgrade me phone.
However, I have a co-worker that's interested in an iPhone, and I've offered to give him my phone for free, and buy his new 3GS when he signs up, as long as we can swap the sim cards and the phones will work just phone. He doesn't care what model of phone it is, he just wants an iPhone, and when I offered to just give it to him for free, he was all down for that.

So will the swapping of sim cards work? What if one of us needs to take our phone in to have it worked on? Will there be issues with AT&T and/or Apple?

 

[JROD333]

Yes swapping the sim cards will work, it's pretty much just plug and play. I did the same when I upgraded my 3G. He will have to get the 3G activated with the sim card that is sent with the 3GS.

 

[bruinsrme]

I do it on a regular basis. no issues

 

[danpass]

the SIM card in my working-perfectly-3GS says Cingular on it. yeah, that SIM has some miles