After a beta period this summer, Missing Sync 4.0 for Windows Mobile is out. This app allows Mac users to sync to Windows Mobile Pocket PCs, smartphones and PDA phones and it supports Windows Mobile 2002, 2003, 5 and 6. Features include:

syncing over USB or Bluetooth

Sync with Address Book, iCal, Entourage

Sync notes (includes a notes app for the Mac)

Sync and transfer images to iPhoto

Sync files

iTunes playlist syncing of non-copy protected music tracks

Call and SMS logging

The app costs $39.95 and upgrades cost $24.95

I've been using the beta version with my HTC Advantage X7501 running Windows Mobile 6, and it worked fairly well.

You can check it out on the Mark/Space web sitez: http://www.markspace.com/missingsync_windowsmobile.php