If you have a poor data connection or just prefer a cellular quality call, simply:
1) If you're on an active call, you can please "Cellular Swap" to convert the call over to Cellular.
2) If you're placing a call from Productive, just LONG PRESS on the personal number or the call record and select "Call Using Cellular".
(1) LONG PRESS any contact or number.
(2) select CALL USING CELLULAR, and
(3) DIAL the Forwarding Number to connect to your contact.