Another good technique to reduce the number of robo calls is to have your PBX answer immediately, and play a fraction of a second of the "number unobtainable" t

Another good technique to reduce the number of robo calls is to have your PBX answer immediately, and play a fraction of a second of the "number unobtainable" tone, which is enough for many greedy "robo's" to give up and move on where as a human will barely notice.