i didnt see too much about the jabra BT110, so i thought i'd post my experiences.

first off, i'm not certain, but i think it only supports the "headset" profile, and not "handsfree". as far as i can tell the only thing i can do with it is answer a call, or transfer a call, and hang up.

its pretty nice because it takes an AAA battery and supports bluetooth 1.2 (mainly this gives you much better voice quality in the face of interference (i.e. WiFi), but it pretty much sucks as a headset for the treo 650.

it has very aggressive power saving... if it's not being used actively it shuts off in about 1 second. this means that your call will never ring in the earpiece. when a call comes in, pressing the button on the BT110 should wake it up and cause it to connect with the treo, but i find that its only successful about 60% of the time... and it can take as much as 2 seconds for it to connect. the other 40% of the time, it requires a 2nd push of the button to connect. after it connects, you hear the call ringing in the earpiece, and then you have to push the button AGAIN to answer the call. needless to say it can be 5-6 rings before you can answer the call. and if you get impatient and press the button a 2nd time, there's a pretty good chance that it will answer the call and then immediately hang up.

so i wouldnt really reccomend this headset. i bought it to use with Skype on my mac, and for that it works pretty well, but the 1s poweroff time is still annoying there too.