I have a Droid X, and I use a pair of woodees classic earbuds with mic.
when listening to audio through pandora, audible, and doggcatcher, the play/pause function of the headset mic button is fine, but when a call comes through that same button should answer the call, or hang up the call too.
it doesnt. it will mute the call, but wont disconnect it. i have not yet fully tested it for answering the call, but i seem to think that it used to.
i am running rubix 1.9.7 rom, i use handcent for messaging (other issues there), and i have uninstalled the stock music player app because it kept launching when i tried to resume listening after a call.