Streams, Voice, and Sensitive Dependence

It is my understanding that the PGP algorithm is primarily intended as a block cypher. Therefore, wouldn't an Outer Block stream cypher be more effective for phone conversations? Both solutions require hardware for a practical (tolerably noiseless) implementation, so there's nothing to be gained by streaming data into a block format. In any case, there has been a lot of recent work in dynamic systems (Chaos), especially in the fast computations of Julia Sets. Has anyone seen a paper on exploiting the sensitive dependance in these systems for pseudorandom number generation?