You would need to find the Nexus One that is AT&T compatible as that has the 850, 1900 and 2100 band. The Nexus One that is T-Mobile compatible has the bands that is 900, 1700 and 2100. If the Nexus One is from Europe and Asia, like the Vodafone ones that will be the 900-1700-2100 one. The Nexus One that is compatible with Canadian carriers like Telus, Rogers and Bell, or Australia's Telstra would be the 850, 1900 and 2100 one.
In any case, the Nexus One that has the 850 band also has the 1900 band.