My phone is the HTC Desire S. I have call waiting enabled. On the original HTC firmware I got bundled with the phone, this meant that when another call was coming through I heard a double-beep twice in the background, and then it stopped. Now that I have installed CyanogenMod 7, I'm getting that double-beep continuing for the entire 20 seconds that the call is waiting, if I don't answer it. How can I restore it so that I just get the double-beep twice and then it stops when a new call is coming through?
AFAIK, CM does not (yet) support to configure it. Issue 5268 at the CM tracker addresses this (yours, i take it?) - so anybody else affected is encouraged to "star" it.
Meanwhile, an app named Call Waiting Configurations might provide a work-around (not sure, I didn't test it myself) until the CM team adds the possibility of configuration. Or you could instead activate the checkbox to "vibrate on call waiting":
Additionally, the following apps might be worth checking: