I got my 640 as a gift. The reason I didn't buy it is because of bad reviews about it does not work well with my Treo 650. However after a month with it, I love it and it works with my Treo just fine. I have about half dozen bluetooth headset but none works better than 640. It is utra light and easy to fit into my ear without the ear clip which is the biggest advantage of 640. There are two reason I did not give it a five star:1. No neck cord to wear around the neck Without it I can see myself lose this tiny headset in no time. I actually had to conver a neck cord from another headset mount on the 640.2. No charger adapter for Treo 650.