I have two numbers on my line, number A and number B. I have two phones, BT 6500 and BT X56. When someone calls number B, I get the number B ring on the 6500, but the number A ring on the X56. Spent some time with BT Chat, who confirmed that the X56 is not compatible with Call Sign, but couldn't tell me how to know if any phone is compatible - it's not in any of the documentation of either phone, saying yes or no. BT doesn't seem to have a list even of its own phones which are compatible. Anyone else solved this problem?