The original device he put in the ear of the first suit's cowl was just a distance listening device, he used to evesdrop on targets from far away, he used it in his homeless disguise watching rachel, then later with it in the cowl outside arkham.
The phone is actually seperate in begins, it's assumed that the TDK suit has an upgraded integrated communications system in the cowl, because he not only listens in on calls and police traffic, but also has direct communications with lucius when he's hunting the joker.
So Begins = Phone, TDK = Headset
So the TDK belt wouldn't need a phone on it.
