josh, swapping SIM cards between phones on Cingular/AT&T is no problem. As long as his Razr is Cingular branded or unlocked, it'll work just fine.
It's Verizon and Spring that tie phone IMEI numbers to individual numbers. I swap SIM cards all the time with Cingular and never have any issues.
I just noticed something funny. 2 years ago AT&T Wireless became Cingular right around the time my AT&T Wireless contract expired. I renewed for 2 years with Cingular and now that that contract is up, AT&T is back, so now I get to renew my contract under the AT&T name
