Can you give a little more instructions on changing the "screen Name" in order to change the call back number.

I have a suggestion on how to make it work possibly better but would require the user to set it up on the google voice site before hand. Can the one ring see what you named your phone as? For instance, the gizmo account linked to my nokia is actually named n810. If theonering can "read" the names of the phones this should be a simple way to determine which to call back.