The article in the Sacramento PRAVDA today linked here says that in tests for eight hours a day over an eleven-day period the program blocked more than 25,000 unauthorized cell phone calls.
I admit I am still not sure how this is going to work. My understanding is that the feds need to authorize this due to various FCC issues. I also wonder how it will affect people driving by on public roads near prisons, or even staff in the parking lots. In any case the program is supposed to be up and running by the end of this year.