The line does ring as it should. Incoming internal calls after 3 rings go to that extensions VM, but incoming external calls after 3 rings go to the GD MB.
I have the line (209) set so that the rec'd # is the extension (1684), If busy:To Prime, and PrimeSet is set to 1684.
Under Terminals and sets, extension 1684 is assigned to line 209, Ring Only, Forward no answer is set to 2251 (voice mail), Forward Delay is 3.