If the following fake recording[1] with the special 3 beeps intro actually works to fool robo-dialers, I'd rather the service do something like that. I also remember seeing a dedicated electronic box[2] that had that recording built-in. You either held it to the mouthpiece of the phone or it was wired in-line between the handset and the base. I'm not sure of the success rate of that device. I wouldn't be surprised if a developer attempted to replicate that device by making an app on iPhone/Android. Again, I'm not sure if pressing a smartphone speaker to the mouthpiece of a handset is good enough audio fidelity to fool robo dialers.
[1] https://www.youtube.com/watch?v=DE4zZwDE7bc
[2] not sure if it was this one: http://www.amazon.com/Privacy-Technologies-TZ-900-TeleZapper...