I have a TMobile MDAIII imported from the UK. It's a WM2003 based PDA
phone. I like it, although I am not a heavy PDA user.
Regarding Exchange -- there are two ways of doing what you want.
1. Exchange 2003 has Exchange ActiveSync which will let a WM2003 and
Treo 650 (PalmOS based) sync with Exchange over a GRPS HTTP connection.
It's pull, not push, so you would need to schedule it to sync every X
number of minutes. The nice thing is that it's free. The cool thing is
that it doesn't rely on your desktop to sync at all.
2. You could use Blackberry Enterprise Server and see if you can get a
copy of Blackberry Connect for your phone. That's a push type of system,
so when you get new mail it gets pushed to your phone as well. There is
also Goodlink (http://www.good.com) which claims to do the same thing.
We're investigating these options for Exchange users at my company,
although it looks like we may stick with Exchange Activesync.