The VM-605's built-in speaker pumps out 3.3W of audio power, which doesn't sound like much but is actually quite loud, especially since it's clipped on a visor that's sitting within a few inches of your head. As a result, there are no problems hearing incoming callers above engine and general traffic noise. The mic also works well to produce clear call quality for those on the other end of the line, which isn't all that surprising given the built-in echo and noise cancellation technology.
However, as well as using its speaker, the VM-605 has another trick up its sleeve; it also has an onboard FM transmitter so it can send the audio from callers to your car stereo speakers. This works in much the same way as an old iTrip for an iPod. First, you press the FM button on the right-hand side of the speakerphone. The VM-605 then calls out a frequency, which you tune to on your car stereo. If this frequency isn't very clear you can have the VM-605 scan for another one by holding down the volume up button. It's an excellent system that works really well in practice, plus it offers the bonus of listening to music or turn-by-turn sat-nav instructions from your Blackberry via your car's speakers.
If all this sounds familiar, it's because the VM-605 is strikingly similar to the Jabra SP700 in terms of functionality. They have different external designs, but under the bonnet, we have our suspicions that they may actually be using the same hardware (we could be wrong, though, as we didn't have an SP700 to hand to make a direct comparison). Nevertheless, there's little to choose between them except for design and price as both work extremely well and are very easy to use.
The BlackBerry VM-605 is a great little device. It's easy to use, has good call quality and the ability to pump callers, music and sat-nav instructions through your car stereo is a real boon. However, it is almost identical to the Jabra SP700 in terms of functionality so there's little to choose between them except price. Currently you can pick up the SP700 for around a tenner cheaper than the VM-605, so if you don't care about the BlackBerry branding it's currently the better value option, but of course the price advantage could always swing the other way in the future.