The scenes involving the cellphone surveillance system tied in neatly with Dent's earlier discussion of the ancient Roman office of Dictator. In extreme emergencies, the Romans gave extraordinary powers to one man, who was then expected to give up those powers when the period of his dictatorship had passed.
In some cases, the system worked well. Cincinnatus, for example, was appointed dictator twice, resolved the emergency, and returned to his farm therefater, making himself a hero to his people. (Byron called George Washington the "Cincinnatus of the West")
The problem, of course, is that not all men are as capable of self-denial as Cincinnatus. Ultimately, as Rachel pointed out in the restaurant, Caesar had himself appointed dictator for life.
Basically, the cellphone surveillance scenes showed that Batman may not have trusted himself with that kind of power--but he recognized his own potential weakness, and knew someone who could be trusted. And by placing the matter in Fox's hands, he ensured that he would be compelled to resign his electronic dictatorship.