at 7:00 i got a call, internal, from a collegue. he told me he is getting fast busy tone. i went over and confirmed it. at the time, there might have been maybe 3 external phone calls at the most. then a few minutes later, it is ok. i have ccm 4.2. the user had 7940G. i have a rouer with 1 PRI backhauled by MGCP. what could be the cause of the fast busy tone?