Since I had to go buy a bluetooth phone to interface with the new cars nav system, I also got to do a little learning about bluetooth and phones in general. Thought I'd share the gist of it.
Bluetooth is a specification for short range wireless networking. It operates in the 2.4GHz band like 802.11B/G, microwave ovens, some video transmitters and some wireless phones (among other things). It was intended for connection of devices in close proximity to each other, such as keyboards/mice/pda's to a PC, pdas to each other, cell phones to each other, cell phone to a wireless ear bud/headset or in my case, a phone and a car computer/nav system.
Without further information, one would think one could buy a bluetooth phone and interface it to another bluetooth device, or that if one had two bluetooth devices, one would be able to have them communicate with each other.
One would be very, very wrong.
Bluetooth simply specifies the mode of communication, the physical act of transmitting and receiving the information.
Vendors can implement (or more likely fail to implement) "profiles" and protocols on top of bluetooth. Typical "profiles" are 'headset' and 'handsfree'.
See this for some more examples of profiles and descriptions
You now have to run the gauntlet: Do the two devices you want to interface both support the profile that allows the interface you want? Have the vendors of the two devices implemented the profiles in a compatible manner? Has any supplier of the device disabled or changed the profile support or disabled bluetooth on the device entirely?
If you have two compatible devices, you "pair" them, which is the basic handshake that then enables two devices to communicate. This keeps your phone from hooking to someone elses earbud when you walk by them.
It appears that two bluetooth devices from the same company that advertise a particular capability will probably work well together. Mix and match and you better look long and hard to see if some 3rd party has tried it and reports it works well.
For cell phones, it appears that cell phone providers other than cingular and t-mobile disable part or all of the bluetooth capabilities on their phones. I dont know why, nor can I even conjecture. Maybe it creates a support problem should the capability be inadvertently used. Maybe it creates a fear of customer loss as a pair of bluetooth phones can download each others feature settings and phone books, making migration to another carrier/phone fairly easy.
Past that, even when there is reasonable compatibility, there are frequent limitations.
In my case, the car supports the 'hands free profile' and the 'file transfer' and object push' profile. Many bluetooth phones only support the 'headset' profile, which wont help at all. A good number support the 'hands free' profile, but are incompatible with the car. A handful support the right profiles, but you cant transfer the phones address book to the car, which severely reduces the ability to do cool things like tell the car to "call 'home'". Some supports the address book transfers, but you have to manually send them one at a time and manually send changes.
Since i wanted a carrier with a good, reliable, cheap prepaid plan that also supports bluetooth phones that would work with the car, I was left with T-Mobile. Of course, the only phone that I can get that does everything I want it to do is the most expensive, the Motorola Razr V3. I heard lots of reports of other workable pairings, but they were frequently annotated "unless its an older version of the phone...unless you dont have the latest firmware...if its an unlocked phone you bought off of some scumbag on ebay..."...etc.
Lexus does offer a 'cheat sheet' of phones that work, however the salesman noted as he handed it to me "this is already out of date and I just printed it".
So now we have a really cool looking phone that is going to spend most of its life in the glove compartment of the car, chatting amiably with the nav system.