Cingular 8525 is 3G. It's like the best 3G phone from Cingular to date..
It should work just fine (but then again, if you have a Windows PocketPC, what's the point of connecting it to N800 to access internet, really).

I suggest get something more simple like the new samsung Sync or Razr V3xx. You can use Cingular's Unlimited MediaNet with it.