That's not what they are looking for (I think). They are combing traditional "traffic analysis" (who messaged whom how often in what sequence - doesn't require that you can read the message) with things like supermarket affinity card records, gasoline purchases, general credit card records, etc to look for patterns that they think indicate suspicious activity. Try going to a different city and not buying your favorite foods - as carefully guarded as you are on the phone you will sooner or later slip up and buy European tooth powder rather than US-style toothpaste. Combine that with traffic analysis, gasoline and airline purchases, and boom! You have a lot of false positives (but they don't care about that).

sPh