Notices

I was wondering if the tablets can be used as bluetooth speakers, where I could plug in standard headphones into the tablet and hear audio from a desktop computer (running Vista) though bluetooth? This is similar to the function of the Sony DRC-BT15 bluetooth adapter.

Alternately, can the microphone on the tablets be used over bluetooth to make voice calls, control speech recognition, etc. on desktop computers?

I did a search and found *many* threads on this topic (here here here here here and here) but all the threads seem to be inconclusive. Some of the threads specifically mention the n800/n810, but all seem related.

I'm sure that once someone gets it worked out they'll get it posted in one of the other threads. If you just want audio from your computer, you can use VLC to stream it over wireless. At least one of your referenced threads tells how to do it.
You could do the reverse and stream the audio from your tablet to a PC, but why not just make the voice call directly from your tablet?

Are the speakers (volume level and sound quality) and microphone (sensitivity and detail) good enough?

Otherwise, it's a project with low (immediate) payoff. But still worthwhile..

http://talk.maemo.org/showthread.php?t=30514
I recommend using VLC and Wifi.