There was a time in my life, where every single time my girlfriend and I were about to enjoy some adult time, my employees would call. Without fail. There has to be some sort of twillo app idea in there somewhere.
We just need to tap into the accelerometer, do an FFT and low-pass on the microphone, and check for a correlation between the frequency of a rhythmic acceleration and the frequency of grunting.
There is actually a project going on at my university that basically does that. It's an iPhone app that takes the accelerometer and sound input into consideration. They guys doing that app are graphing the data and have an algorithm rating the "performance". It's supposed to be a little criticism about the current state of privacy (and it includes abilities to share your scores in Twitter and Facebook :) )
Reminds me of this best man who setup a Twitter account for the sole purpose of automatically tweeting when the newlyweds were having sex (recorded using a pressure sensitive device):
