Does anybody know if it is possible to upgrade the bluetooth for headset use?

Unfortunately, no. However, I have heard some web sites speculate that Nokia could, if they wanted, include a headset profile in a firmware upgrade.

A friend of mine was considering the 7650 but was turned right off when he heard aout lack of bluetooth headset compatibility. Not to worry though, I have two sales under my belt for the 7650, possibly 3 and maybe 4!

Nokia should be paying me commission!