Be Weary...
Be weary of most of the Windows Mobile phones. Most phone companies are going to be getting rid of most of the opperating systems and switching them to Android. (a friend of mine works for AT&T and he said they are coming out with 4 new android phones in the next couple months) I have T-Mobile and have had just about every smart phone they have except for the Nexus One (which I would love to have!)
I just recently had the HTC G-1 and I had nothing but problems with them. They since then, switched out my phone and gave me the Motorola Cliq. I love this phone and has been the best phone I have had with T-Mobile (and after being with them for over 8 years) other than my old school blackberry.
I also, have a client that I work with and he owns a company that deals with the programming aspect of cell phones and he said that most of the carriers (Including Blackberry) are going to begin running android in the very near future. Just something to think about, anywho, good luck with your search.