If I remember correctly, Cingular uses
GSM (same as T-Mobile). The PEBL is also a quadband phone. I don't see why it shouldn't work.
I bought an unlocked PEBL from eBay a year ago for my dad. It's an ok phone. I much prefer the KRZR I have now. For some reason, his PEBL keeps receiving unknown text messages that contain weird characters at times. I think it has something to do with it being unlocked. In either case, make sure you really want the PEBL before buying it.