[brianpgordon]

"Unlimited" plans just hope that not too many people use a lot of data. But if you're really one of the people who doesn't use much data, you might as well use a plan which charges per gigabyte, and then you're exposed to the real per-gigabyte cost. Market forces therefore keep the cost of unlimited plans roughly in line, and the per-gigabyte cost is still relevant even for unlimited plans.