Good luck.
I tried a GXW4104 and ran into this really weird issue where if say FXO 1, 2, and 3 were in use and FXO 1 hung up -- FXO1 wouldn't free up / hang up and would stay in use until FXO 2 and 3 hung up.
Another example would be if FXO 1 and 2 were in use and FXO 1 hung up -- FXO 1...