I found the Q1 to have the most robotic, digitized sounding voice quality, of the headsets I tried. I actually felt (for me at least) the Sound ID 400 was hands down the most comfortable. I guess it just depends on one's ears.
The Plantronics 975 had great natural sounding voice quality, the best of all of them except the Voyager Pro. And it had a nice fit. But as I said I can't remember if it had the connection issues the Voyager Pro has with my N86. And it wasn't so great at noise cancelling (at least in cafe settings with background music and other people talking).
In many ways I actually felt the Motorola HX1 in regular CystalTalk mode had the best noise cancelling and it connected up with the N86 really well. But I didn't like the fit on it, because of the way it goes into the ear canal for the bone conduction thing. And the volume in the earpiece was a little low. Still, if I was going to have this style of small bluetooth headset, I'd probably look for another Motorola with CrystalTalk and a more normal fit. Except for the fit issue, all around the HX1 was the best of the small discreet headsets that I tried. That and I still think the 975 is worth trying, if you can return it if you don't like it.
The 3G on T-Mobile is not going to work at all. The 2100 is misleading, but it's not the same thing.