I have three 7960 phones that came to me from different sources. Im registering the phones with a UC540. The phones load there relevant files and I can make calls using the speaker, I hear dialtone and I can make a call. However if I attempt to make a call using the handset there is no dialtone and the display does not indicate that the phone is off hook? Its as though non of the switch hooks are working on all three phones. Am I missing some thing as far as configuration?