[cvwright]

Hey, cool. Always nice to see this work show up on HN. But I don't think this is the paper you're looking for. In '08, we could only spot phrases that we knew in advance, and they had to be at least a certain length.

The most impressive results -- going from encrypted VoIP to text -- were done by Andy White and others, a couple years after the paper you linked above. It's this one:

A.M. White, A.R. Matthews, K.Z. Snow, and F. Monrose. "Phonotactic Reconstruction of Encrypted VoIP Conversations: Hookt on fon-iks." In Proceedings of IEEE S&P, 2011. http://www.cs.unc.edu/~fabian/papers/foniks-oak11.pdf