Talking on a speakerphone--and not with an ill-fitting headset--certainly makes a 45-minute conference call on your evening commute much more manageable. Nevertheless, you should be prepared for a couple of drawbacks. First, most speakerphones have illuminated buttons or blinking lights, and their flashing can drive you nuts, particularly at night. Second, leaving the speakerphone perched in your car is convenient, of course, but--depending on where you park your wagon--you run the risk of drawing the attention of thieves. (And if you are thinking about purchasing a windshield-mounted unit, remember that it may be illegal in your state to attach any device to your windshield.)

Lastly, for your Bluetooth cell phone to play nicely with a Bluetooth car kit, your phone needs to support both Hands-Free Profile (HFP) and Handset Profile (HSP). For more information about Bluetooth standards and profiles, and for advice on how to choose the right devices, read our .