Comment Re:Spoof the line as disconnected.. (Score 2) 497
It's sometimes called "the triple tone."
http://en.wikipedia.org/wiki/Special_information_tones
There's live samples that can be played there. IVR systems automatically detect the no circuit tones and removes or deprioritizes a number.
Playing the wikipedia sample by holding the phone to the PC speaker should be enough, I recon.