What usually saves my bacon is ProComm or Hyperterminal. If I can show that the data got to the back of the PMS, it's someone else's problem... "look, I can read it on my laptop, you just called 1 800 852 4632."

My money would be on someone kicking at the tangle of cables just as a data string is going by, and the system never gets "End-of-text." So the dataset locked up, wouldn't let go.

I have also, in desperate times, done Fred's pull-and-delete-quick trick, but usually only after I get pissed off and decide that I'm the boss, not the PBX.