If it helps, we can do this on the HPTouchpad and N900. Granted the telephony connection is through Bluetooth so the range is limited to the next room in the house.

The TP has its own dialpad and contacts list to allow you to make and receive calls remotely. Then you have vnc to operate other functions on the phone if you wish.

Not sure if this is relevant tbh, but it could be worth a look into to see how other devices do the virtual phone thing