Demand of criminals/journalists/activists/curious\ people seem to dictate the price. Think of a repressive regime hunting down the opposition. They track every phone via cell tower handshakes and map out individuals using "metadata".

With calls and SMS you can login/register on apps/services and when doing so "reset" towards a fresh profile if done right. That's a new dot on the map. With internet you can only access these services.

That's just my guess though.