I've been using this for more than a year and has been using it ever since. The mouse itself is very small and comfortable. Not as comfy as those curved ergonomic Logitech mouse, but comfortable enough to use for long period without wrist pain. The symmetrical shape also allows lefties to use the mouse. The mouse features 800dpi of optical precision. This should be sufficient for general purpose computing.
The VoIP part works with no driver needed. When receiving an incoming call, the LED on the top lights up. Flipping it open (like a standard clamshell mobile phone) answers the call. Pretty simple eh? As a bonus, the scroll wheel even doubles as a volume control! Flipping the lid halfway activates the loudspeakers if you fancy that sort of thing.
I got mine for £20 and find it worth the money. I question whether it is worth parting £50-60 for a mouse that moonlights as a VoIP phone. The sound quality is pretty good with the latest Skype program, on par with most landlines and mid-range mobile phones. However sound quality on Skype highly depends on your connection and ISP bandwidth availability than the mouse itself.