is there any reason why there isn't a "call forward on busy" feature available on voipo?

A version limited to voipo-run numbers as the destination would work for me.

Background:

we have the stock voipo cloned line setup, where both line 1 and line 2 ring simultaneously and the call goes to the line that picks up first.

Unfortunately, our current two-line phone goes deaf & silent when the 2nd line keeps ringing while the 1st line is picked up -- and that seems to happen most of the time when someone calls our number.

It would work better for me if we could set things up so that, if line 1 isn't in use, only line 1 rings; line 2 would only ring if line 1 was busy.