As someone who listened to the big multi-agency training exercise and disaster scenario Operation Badger One last week, not once did there seem to be a breakdown in communication, nor did any of the response teams mention experiencing any difficulty in communication during the exercise.
I used to live in Ohio where they have a big multi-agency communications network MARCS, and even with that in place for several years now the various departments have intra-state communication errors. I think that the idea of a statewide communications network works great on paper, but there's too many obstacles to have a flawless system. Even if there a state had the best communications equipment and network in the world, the people using it are going to make mistakes, either in planning, design, and/or operation...especially in the event of a real and sudden emergency.