The owner's manual of any modern car is a festival of disclaimers. Your satisfaction with seat belts, child seats, gas mileage, and even the car's likelihood of outlasting its lease all come with exceptions and exclusions. So it should be no surprise that most Bluetooth-equipped cars have a little note regarding that wireless technology. The warning suggests that you verify your Bluetooth phone's compatibility with the car's Bluetooth system. Huh? My PC needs no such disclaimer for its USB support nor does my Wi-Fi router for 802.11g compatibility. And even so, exactly where and how am I supposed to verify that my Bluetooth phone and my Bluetooth car will like each other?

Bluetooth revolves around two sets of specifications. One defines the radio frequency (RF) portion, the actual low-power radio that sends information back and forth. The other specification is a set of instructions called profiles that allow Bluetooth devices to accomplish certain tasks over the network. These profiles cause the headaches.

The Headset Profile was the first Bluetooth profile that supported hands-free calling by connecting a phone to a headset. It has no accommodation for fancy functions such as dialing or on/off hook control; it's just a dumb conduit that moves audio back and forth.

Then came the richer Handsfree Profile, which is the technology installed in most cars today. It took the Headset Profile's ability to move audio back and forth, then added voice recognition, on/off hook control, and some information transfer, such as call duration. Yet while carmakers jumped on the Handsfree Profile, many phones run the older, simpler Headset Profile. This disconnect can leave you in the irritating and costly position of having to buy a new phone to go with your new car.

Mike Foley, executive director of the Bluetooth Special Interest Group (SIG), estimates that 90 percent of cars will have Bluetooth long before 90 percent of mobile phones. "This is simply because a car is a much more expensive product and can absorb the cost of the Bluetooth solution a lot more readily than a $49 phone that a carrier ends up giving away with activation," he said. So the rather glacial car industry is arguably savvier about Bluetooth than the wireless phone business that helped invent the technology.

Now, just when this sounds semigettable, let's look to the future.

More cool innovations, more annoying incompatibilities
Car companies want their in-dash Bluetooth system to free you from looking at your phone for ultimate functionality and safety. But as things stand now, most Bluetooth-equipped cars require you to glance at both your phone and the in-dash LCD. The car's display typically shows the dialed number, as well as call status and duration, while your contacts and the keypad--which you may need to use for touch-tone services--are on the phone. It's a hodgepodge of interfaces and distractions.

Enter cars such as the 2006 Audi A6, which offers a Bluetooth system that uses a new Phone Book Access Profile. It lets the car import your mobile's call data as you get into the car; missed calls, favorites, recent calls, and so forth all get populated into the in-dash LCD. Eventually, your mobile's entire phone book will be transferred to the car, once the in-dash memory is large enough to support the ever increasing capacity of today's smart phones. And the Bluetooth SIG tells us to look for BMW and Toyota/Lexus vehicles to sport phone book access soon, as the technology is being baked into an official spec.

And some carmakers are using an even more ambitious Bluetooth strategy involving what's called the SIM Access Profile. With this Bluetooth scheme, your vehicle has its own built-in phone that instantly copies the GSM SIM card info from your mobile when you get in the car. It then disconnects your mobile from the network and takes over the connection. When you make calls, they are conducted entirely from the car's built-in hardware; your mobile phone is just a dead lump of silicon until you get out of the car. The benefits of this scheme include never having to charge your phone in the car or worry about it dying, and a built-in car phone can use an optimized high-gain antenna and heartier RF power levels. The end result is a premium communication system.

With all these advancements, buying a car with a Bluetooth system is going to be a little like buying a PC in the '90s--something new is always just around the corner. Still, go forth and buy that new car; even at its most basic, the in-car Bluetooth hands-free systems are really very cool. If you're buying a new car, take those few minutes while the salesperson "checks with my manager to see if he's willing to lose money by selling you the car at that price," and head over to the service desk. Ask them to check if your phone works with that specific car, and have them run off a copy of compatible phones, especially if you're going to buy a new phone soon.