The second button is an "FM switch" which tells the device that you want to route music or calls to an FM frequency. And the third and final button, a volume up/down switch, adjusts volume levels and also lets you select different FM frequencies when connected to a car stereo or other radio.

Battery life was very impressive. I hooked up the device to a radio within my home, and it ran for more than 12 hours straight, transmitting music from my BlackBerry, before I shut it off. I've probably used it another hour or so since, as well, and it still has power.

Call quality was good, as well, both on the speakerphone end and the call recipient's side of things. Only one person I called commented on call quality, saying I sounded a bit distant and "tinny." Most folks had no idea I was using a speakerphone until I specifically asked them how I sounded. I liked routing calls through my car's speakers. But you can also use the unit's internal speakers for calls, so you could, say, employ your car's CD player while making a call via speakerphone.

Perhaps my favorite thing about the BlackBerry Visor Mount Speakerphone is that it works along with GPS navigation apps like . And not only does it allow you to listen to music or place calls while following on-screen driving directions, but also routes voice directions through your car speakers. This is huge for me, because I listen to my music LOUD, and that means I can't normally hear driving directions while using GPS. With the BlackBerry Visor Mount Speakerphone I can, and that takes my GPS apps to a whole new level. (Note: I only used TeleNav along with the speakerphone.)

You can you listen to music stored on your BlackBerry, or play music from satellite radio applications like Pandora through your car's speakers.