I am looking at buying a X10

[#1]

I have noted that on the SE site there is only one version. Is there a X10a or will all X10's support HSDPA 850 / 1900 / 2100 for USA?

[#2]

Yes, there are actually 2 versions of X10 that can be used in USA.

The one I'm using is:

X10i = HSDPA 1700 = T-Mobile USA 3G

In your case you'll want a:

X10a = HSDPA 1900/2100 = AT&T 3G

X10a can be found in Canada (Rogers network). I'm not sure if there are non-branded X10a in the market yet.

Try eBay... (you'll also get 8% off using Microsoft Cashback + 1%-2% eBay Bucks). Make sure they say it's for AT&T 3G.