The Audiovox 5600 is a great phone. Microsoft Smartphone as an OS does work well. Its actually a newer version on Windows CE.
Outside its normal functions here are some that of the thing I do with it:

VNC - remote control any PC with the VNC client
MS schedule - for my meetings at work
GPS - Microsoft Street and MAp with Bluetooth GPS locator
mp3 player - you need to have 512 megs of mini SD memory
i use it for storage - carry all my utils on it for any computer proggies
MSN messenger
Bluetooth Headset works well with it
TXT message
task switcher to kill any lingering memory hogging programs

future things I have yet to try:
MAME emulator
remote control
unix terminal
usb devices like keyboard, wifi,

thing you need to do initially:
create a LOUD ringtone and save it in storage. All standard ringtones are very quiet.
buy a clear plastic screen cover
what its missing:
WIFI