Telephone companies like unlimited local etc. calling because they've found that tracking each little usage of a minute here, fifteen minutes there, for all of their subscribers is not worth the cost of the bureaucracy and systems needed. They are then renting the line, not any physical good that can diminish, like water or electricity. It's much the same situation with ISPs. Their tiered plans have rates ridiculously profitable, and if those rates were brought back to something reasonable for the cost involved, flat plans would still be attractive for everyone involved.