Voip is definately doable with BT HSP. Note that HSP doesn't support such advanced remote control mechanisms as HFP or AVRCP would. Quality of the SCO link that HSP uses for voice ain't that great, though (*insert standard disclaimer on how people perceive quality*)

While A2DP (this is the good quality stereo audio profile) is not officially supported, by checking on [public] development on BlueZ it's quite easy to get around to what the current state is and how to configure it on.

If you have specific technical questions regarding this, asking in the mailing list might prove useful