1. Regular press would work just like it does today, i.e., brings up the phone dial pad.
2. Extended press would activate voice dial.
The behavior of the key is for calling so, why not provide the second feature. Is this possible? Is there an app that will do this?
I know there's the convenience key that can be assigned to voice dial but, this would free that up. And, this seems more logical.
You can use an app like extra keys or sixtools that adds extra convenience keys to the volume up, volume down, and mute keys. Other then that I don't believe there's anything out there like what you want.