How do you mute your ringer while you are on another call? This is particularly a problem for users with headsets. If they are on a call and another call rings in, the ringer blasts right through their headset and they cannot hear their current conversation.
The majority of our users are taking calls through the softphone on their computers.
This is a major issue for customer service agents and sales representatives who typically have multiple incoming calls at once.

Suggestion - You could try disabling call waiting within your incoming call settings. Disabling call waiting should only allow one call to be place to your phone at a time. (settings, phone, incoming calls, call waiting <ON/OFF>)