I bought a USC Nokia 3360 on eBay once.  Not only was it SOC locked
(which wasn't a problem- Cingular overcame that with an OTA update)
but also all data service (WAP) functions were removed (USC doesn't
support data on TDMA.)

Shouldn't be a problem for AT&T or CallPlus use (no TDMA data there
either), but I wouldn't use it for Cingular if you want WAP
functionality.