asterisk users - Jun 2006 - call rejected tone within dialplan

Hi all,

I am attempting to work through some oddities with PRI signalling to
neaten a few applications up and am having trouble sending a cause code
1 (unallocated) signal from within a dial plan. If I make it so that the
dialled number does not match an entry in the plan I get the correct out
of band continuous tone but calling SET(PRI_CAUSE=1) followed by hangup
presents an engaged tone. I would have expected both to act in the same
way ?

Anyone got any ideas ?

Tristan.