Try looking here:
http://www.securemalls.com/cellphone...oducts_id=2182
The page references the 800W but clearly states the adapter has no microphone connection, so taking a call will not work. But it does say that is is compatible with the Treo 800w.
As a side note I am looking for a way to modify my 800w's charging cradle so I can listen to music, videos, etc, while working at my desk but not sure how the treo is aware when a headphone is plugged in. (If you notice when you plug in the headphone while playing audio, it takes a few seconds to shut off the speaker and redirect the audio feed to the headset.)
There are five wires coming from the micro USB-B plug on my cradle; Red, White, Green, Silver (uninsulated), and Black. The Silver and Black are tied together into the circuit board (to ground). My guess is the Treo audio circuit detects the impedance/voltage drop across the headphone coil and does the switching electronically.
I would suspect if the adapter I listed above meets the USB 2.0 electrical specs then it should work on the Treo 800w as well. However, I have read forums where the response is that these do not work:
http://discussion.treocentral.com/sh...d.php?t=172670
If you want to try this adapter, this is the cheapest I have found so far:
http://www.wirelessground.com/mircousbhfadap.html
Hope this helps.