With the Treo 650, after the phone rings about 4 or 5 times, the earpiece finally starts to vibrate, but no caller ID is shown at that point.
Once, I actually saw the caller ID and the earpiece ring at same time the phone rang, but in general the earpiece doesn’t respond to the Treo signal soon enough.
Thirdly, the earpiece starts powered down after taking it off the charger. Also, the earpiece powers down after sitting idle for a couple of hours, even though it has a full battery. The buttons feel kind of cheap for a $100+ item.
As noted in comments here, Jabra doesn’t seem to have a good track record of producing workable earpieces for the Treo.
As seen here, other bluetooth headsets out there for treo, I would choose the Sony Ericsson HBH 662 for the size, but none of the headsets reviewed stood out for small size, talk time, standby time and sound quality.