Try it! I'd love to see that work. I thought about doing it myself for unit testing.
That seems like an awfully complicated way of doing it, why not use a digital voice recorder (your pc/cellphone) to record each set of beeps and play it back.
Tried it, didn't work. I do have a crappy phone (though the digital recorder is quite good).
I think you could actually build a Twilio app to cheat... if only there were more hours in the day, I'd try it!