I don't get any telemarketer calls, but quite a few of what is known as "missed call" ads. I never thought they were doing it on purpose, though. Despicable but admittedly clever spam.
"'Missed call' marketing is the term that has been given to the practice of calling a mobile telephone for such a short period of time that the owner cannot answer the call. When the marketer disconnects the call, most mobile phones present a 'missed call' notification with the marketer's number. The marketer intends that the owner of the phone will think that they have missed a legitimate call and ring the number back, in which case they hear a recorded promotional message."
-- Cellular News via Textually
