In my research today, I discovered that the 640 or 645 is the unit with the charging problem. The 655 seems to have fixed that problem.

For Blackberries, the 655 has a several second delay in answering calls. However, there is a specific Blackberry version that is supposed to come out shortly from RIM that fixes this problem. I may wait for it.

It seems that Motorola's have volume and other problems but that there is a lot of variability -- some units connect to a specific phone well and some don't. I haven't seen any logical explanation as to why that might be the case.

Has anybody used the Plantronics 510? It is a somewhat older, bigger model, but seems to have gotten good reviews.