And even the two GSM carriers (T-Mobile/AT&T) have different frequencies for 3G, so even though you can move an unlocked Nexus One across their voice networks,

And even the two GSM carriers (T-Mobile/AT&T) have different frequencies for 3G, so even though you can move an unlocked Nexus One across their voice networks, if you want 3G your choice of device determines your carrier.