unlimited cellphone

Why are there no providers that give unlimited cellphone usage for a flat fee. There is even such a thing for data on a cell phone. Could it be b/c the business is in people going over their minutes? Or because the bandwidth costs would be too high if people used their phone too much.

More interesting question: how much bandwidth does a cell-to-cell conversation take?

Probably more important is that a given network probably charges all other networks to deliver data within itself. ie verizon charges tmobile in order to make a call from a tmobile phone to a verizon one. I wonder if flat-fee unlimited is doable, though...

I think such a provider would make a killing in its first few months of appearance and then the rest of the providers would need to catch up.