I have 1 x BT  Dect Telephone: BT4500, 1 x RTT 56 A (1000 Ohm bellset) and a wall mounted Bellset 50E (4000 Ohm) connected to a PAP2T ATA. As currently configured, I can make and receive VOIP calls. However, If I add an additional Phone: GPO 332 (100...