Hi Anthony,
just an update to say that the change you made works perfectly!

Just to outline, Using javascript I first set a scheduled broadcast for x seconds time (which in this case will also end the call).  If something occurs before this broadcast, the broadcast should be canceled. 

To do this I used the following javascript:

//set the broadcast to play and then end the call
session.execute("sched_broadcast", "+60 playback!normal_clearing::/sounds/callending.mp3 both");

//I now need to get the task ID for this broadcast
var endCallBroadcastTaskID = session.getVariable("last_sched_id");

//now check for something. if something happend then cancel the broadcast using the taskid collected previously
if (somethingHappened == true)
{
    session.execute("sched_cancel",endCallBroadcastTaskID);
}

I will happily add to the wiki to include this change/addition, but will need a few pointers in doing so.  Is there a page on the wiki explaining how to do this?

thanks
Matt