I have the HTC Touch Diamond, the lesser version of the HTC Touch Pro on Sprint, aka the HTC Fuze
on ATT. Essentially its the same device sans keyboard and MicroSD storage. Beyond that the two phones are basically identical
This phone rocks! I can stream my shoutcast radio stations for the office and in the car, mycast all my videos and MP3s from my computer to the phone in real-time via Orb (either through the web interface or Kinoma FreePlay
), RDP and VNC into my machines at home, take awesome photos with autofocus then upload them to Facebook, and browse the full web with Opera Mobile 9.5 beta (pre-installed). Very nice integration into Gmail's IMAP service, and of course Google Maps works a treat too. You can also put Garmin or TomTom on for step-by-step voice navigation, and even broadcast your GPS location live on Google for anyone to see using the free TrackMe
Very large communities are built around these HTC phones at both XDA-Developers.com and PPCGeeks.com with a bunch of hacks, tweaks, and custom ROMs available.
Really, the only thing the iPhone holds over a Windows Mobile phone IMO is gaming (just buy a Nintendo DS) and Pandora internet radio. There are some decent homebrew games though on XDA-Developers, plus there's always ScummVM and Zork!
Finally, you get copy/paste support and the ability to write/edit MS Office documents on the go. Try that on an iPhone, nyah nyah