[Asterisk-Users] Special "error" numbers

[Asterisk]

Are there any special numbers in the UK that are "not available" "busy" 
"congested" etc so that I can test to make sure that I am playing the 
correct tones back to the user ?

At the moment, I am getting a boatload of "reorder" / not available when 
  I know that the line was "engaged" or "busy". Trouble is trying to 
track  it down because the line is not always "engaged".

Does BT have any special numbers to call ?

Julian