Any details on the crash?
are the phones on the same subnet as the NBX still getting dialtone???
is voicemail and auto attendant operations still working.
First place to look is to connect a console to the NBX.. when it "crashes", do an "i" command.
Is anything in SUSPEND mode (other than the debugger process)
You should also do an InetStatShow and post it here
That is a beginning...