I briefly toyed with the idea, but the steep cost of the add-on made me hesitate...
That is, until I bought a BMW X3 for my wife, which had integrated bluetooth capability. Wow. It is simply the best hands-free operation available. Whenever the phone is in the car (or very close proximity), a wireless link is negotiated between the phone and the car. The phone book downloads from the phone to the radio, and all functions are controllable from the steering wheel (call, answer, hangup, search thru phonebook). Incoming or outgoing calls automatically mute the sound system for the duration of the call, and the sound quality of the call through the speakers is crystal clear (as is the sound quality on the other end).
I don't know if the Mobile-Ease product is as comprehensive or has the same quality as BMW, but if it does, it is well worth the price. This is the only hands-free cell phone option that I have tried that is worth using, and in my opinion, is a necessity with the manual transmission.