I have the bluetooth transmitter for the computer.
A few years ago I chucked the cash down for a SonyEriccson T-68i specifically to have my address book saved in more than one spot should the SIM card or phone become damaged. I found bluetooth to be good for much much more.
The other added bonuses were thru Clicker
http://www.salling.com/ my computer recognized when i was in the room, would turn off my screensaver, make my away message on chat programs go away, turn on my mp3 player. From the OS I could reply to text messages using the full sized keyboard, answer the phone (caller ID on screen) with the mouse nice when the phone is in the pocket and i was on the headset and pause my music or turn it down until i ended the call.
This all macintosh wizardry, I don't know how well windows integrates bluetooth or if there is a comparable application to Clicker. Part of the nice thing about Clicker is that it uses AppleScript, which is easy to learn to write and is very versatile, so making your own functions is a snap.
edit:
Apparently, they have released a windows version of the software for XP. Yes buy the transmitter and this software you will be impressed with the $50 you spend on the USB transmitter and Clicker. It will make your bluetooth phone the coolest geek toy ever purchased.