AT&T operates a casino. You bet on how many minutes you’ll use. If you use less, they keep the extra money. They win. If you use more, those cost 50 cents per minute. The house always wins. It’s a great business model if you can keep it up.
Last month, I went way over on minutes. AT&T’s staff switched last month to a different billing plan. The house gave up its edge. Yes, this is also evidence that they win enough either way.