Add option to mute incoming call ringer while on another call Merged

the app rings VERY LOUD while i'm on another call and if i have someone on the phone and i'd like my assistant to possibly grab the call, i have to sit there an let it ring or push it to voice mail. I'd like the option to mute that call ringer, or to simply have a more subtle beep or tone (like other phones have = call waiting beep). This is much less intrusive to my current call.