All of the headset's functions are controlled with just two buttons, both hidden towards the rear. One in effect comprising the back curve of the Prime and the other sitting just behind the status LED. A single press of the forward button will answer an incoming call, pressing and holding for two seconds turns the Prime on or off out of a call, or activates the noise reduction function in one (why that's considered useful I don't know; it's too good to want to turn off).
A single rear button press will refuse an incoming call, or cycle through volume levels and a two second hold in standby activates voice dialling on any handset that supports it - which my iPhone annoyingly doesn't.
You may notice from the images that the Jawbone Prime features the same Voice Activity Sensor (VAS) as debuted with the Noise Assassin - that clear rubber blob at the business end of the device. As before, this presses against the wearer's jaw enabling the Prime to sense when its user is talking, so that the microphone is turned off the rest of the time; cutting down on the level of external noise transmitted. The Prime also boasts a number of noise reduction algorithms which purport to further distinguish speech from external interference and just as with the Noise Assassin these work famously.
Certainly neither of the two people I called were any the wiser that I was doing so with a hand free headset in a car. Okay, so 40mph in a Fiat Panda isn't exactly going to stress any noise reduction circuitry, but I'm entirely confident that I could have been in a McLaren F1 or a Ferrari 430 Scuderia and had concluded my conversations just as unhindered. Importantly clarity at the Prime's end is also great, although the volume seems to have an annoying tendency to reset itself to the minimum occasionally - I'm inclined to blame my iPhone 3G for such issues though. If only so I have yet another reason for needing to upgrade to an S.
The Jawbone Prime also touts great wind reduction and winding down the window in my car confirmed that, yes, it does indeed work pretty well. It is, I am reliably informed, effective enough that speech is still perfectly clear, although wind noise isn't eliminated, simply reduced - not that I'd expect anything else.
The Jawbone Prime is, like its predecessors, fairly expensive especially when Bluetooth headsets are considered something of a commodity item. However, it looks great, works fabulously and emanates an air of desirability that's hard to resist. If you can afford one, get one.