Here is my mini review of the Plantronics 655 vs the Plantronics 510, for those of you trying to decide which one to get. Note: Both headsets were used on a Blackberry 8700c

655 Pros
Very small & Light, fits in pocket nicely. Even in lipstick holder
USB Charger uses same USB cable as the Blackberry USB Cable so no additional charger needed
Battery Charger is a nice addition if you don't have access to USB or an Outlet
Volume is nice
Fits in ear nicely, no need to hook over your ear
Easy to put on with one hand

655 Cons
Picks up WAY too much background noise. Using this at the airport, resturant and the mall, the person on the other end would complain that it was way too noisey.
Battery life is extremely short. I averaged about 2 hours of talk time.
The way the ear nub sticks out of the lipstick holder, while you have it in your pocket the ear nub could fall off
Buttons are hard to push and you will pratically shove the heatset in your ear trying to press the buttons. Luckily volume and mute can be controlled by the phone
Slow Sync time with calls. About 3 seconds

510 Pros
Very good noise cancellation. While in the mall, airport and resturant, you could barely hear the noise. Even outside in downtown NYC you could not hear the traffic. The noise cancellation isn't perfect, there are times when it picks up noise like the hotel guy blowing a whistle to catch a cab but the noise cancellation is 100x better than the 655.
Folds up nice to fit in the pocket
Battery life is really good. I use it off and on for 2-3 days without needing a charge
Volume is louder than the 655
Priced better than the 655
Faster sync time with callls. About 1 second


510 Cons
Hard to put headset on with one hand. Unfolding and putting it on with one hand is nearly impossible. I just unfold it and stick it in the cup holder before I start driving .
Seperate charger. Does not use the same USB Cable as the Blackberry.
Bigger than the 655 so not as much room in your pocket
Buttons are hard to push and you will pratically shove the heatset in your ear trying to press the buttons. Luckily volume and mute can be controlled by the phone
Loses connection to phone every so often.. don't know if this because i'm accidently pressing the headset power button while it's in the pocket.

I sold the 655 and kept the 510. I miss the easier to put on and small size of the 655, but everything else, the 510 is way better at. I hope this little comparison helps you if you are trying to decide.