Ugh, Can't use it in my area of Canada. Need AT&T compatibility. Damn you, TMobile.
Quad-band GSM: 850, 900, 1800, 1900
Tri-band HSPA: 900, 2100, 1700
HSPA type: HSDPA (7.2Mbps) HSUPA (5.76Mbps)
AT&T doesn't work on any of these bands in your area? Which frequency do they use?
It's a little odd that a phone which clearly has the antennas to run on 850 and 1900 can't use them for 3G. (Yes, I know it's common. It's still odd.)
AT&T doesn't work on any bands, period, in the poster's area - he's in Canada. Rogers, Telus, and Bell in Canada, and AT&T in the US, all operate HSPA (3G) networks on the CLR and PCS (850MHz and 1900MHz) bands.
900 and 1800 are Europe only GSM and DCS bands. 2100 can mean either the European IMT band or the US/Canada AWS band. 1700 denotes that US/Canada AWS band.
Anyways, it appears that the Nexus S only supports the GSM, IMT, and AWS bands for modern wireless communications (HSPA). That sucks because it means that in Canada you're stuck with Wind Mobile who have a terrible network.
TL;DR
The Nexus S isn't much of an option in Canada. Thanks, Google.