I tried a couple different bluetooth headsets (Plantronics) for VOIP with my MBP and they sucked...they'd work as long as you didn't move more than 2 feet away from the computer. Even turning your head away would cause static/interference.
Tried a USB headset, also from Plantronics - also crap.
Hmm...maybe Plantronics is the problem here...although the BT headsets both worked fine with my cell.
Anyway...in my experience, using the built in MBP mic/speakers (or earphones and built-in MBP mic if you want more privacy) worked better.
If anybody finds otherwise, I'd love to hear about it....