This was confirmed today by head spokespeople at both Cingular and Nokia USA.
It'll still work fine on the whole 2G network - including EDGE - you just won't get 3G in a small handful of 3G cities.
1. There will be more higher-end phones in Cingular's 3G lineup. (QVGA display and a few other features place this a notch above the CU320.)
2. Nokia can still be part of the first phase/wave of Cingular's 3G lineup (sort of).
I wouldn't be surprised if later on they replaced it with a 6282i that adds WCDMA 850. I don't have any specific info that this is the case... but it would make sense. It would certainly be consistent with what they've done in the past (like the 6340i and 6590i).
They told me they will be launching WCDMA 850 in a handful of cities this year. The bulk of their 3G network will definitely remain 1900 for now, but I believe in some cities they are constrained by the spectrum licenses they own, and they don't have a choice.