According to the Tim Pettitt video featured on front page, just need a bluetooth connection. I am not certain from the video, but you may also need both devices to be one the same profile.
^It probably depends on how it is set up. It's possible that for call forwarding the phone just treats the touchpad in the same manner as a wireless headset and therefore wouldn't need to be on the same profile (or for the phone to even be running webos).
I suspect though that forwarding of text messages may not be possible without a software update and given how HP have treated legacy devices so far I very much doubt that is coming.