I have my Cisco 524 phone connected to my UC500. It has two lines active at the moment. One of the line is private and the second line is shared with another 524 phone. I have received complaints from other colleagues that my private phone line is busy while there was not any active call on either of the numbers. I even tested that my self by ringing my private number from my mobile phone and I got the same busy tone whereas there wasn't any active call on the private or shared line whatsoever. Can anybody suggest me some solution on it? Many thanks.