I bought the Jawbone II at a Sprint store when they told me it was the best around in blocking out ambient noise. I am told by callers that it does sound fine. However, the device does not stay in my ear with any of the ear pieces, even the new odd looking ones that they now have. Because of that, the tip never keeps contact with my jaw or cheek, resulting in poor voice transmission to the people with whom I am speaking. Worse yet, is a real design flaw. When the unit comes loose, it is difficult to put it back into the ear tightly without turning the unit off and hanging up the call. The on/off button on the face of the unit is exactly where you have to press to insert the unit back into the ear.
Also, when I ordered the new "Newfit Earbuds", they send them for free, but charge $2.99 for shipping via UPS 4-5 day ground. No problem - seemed fair. They arrived about 8 days later in an envelope sent US mail with a $0.42 stamp! These Newfit Earbuds do not work at all to keep the unit in place. I am going back to a corded earpiece.
If you are thinking about buying one of these, I suggest that you INSIST on trying it for fit in your ear before shelling out your hard earned money. Unfortunately, I paid $140.00 for my unit last fall and I am now throwing it away.