AT&T's cost for their Mobile share with unlimited talk and text. Their prices go up for the amount of GB you have, 1 GB is $40 plus the cost of the smart phone $45 then another $15 for every extra GB you use. The prices are all in a range between 1GB and 20GB.(20GB cost is $200 not including phone and extra GB)
Verizon's prices go by the same rules 1GB is $50 plus which ever device you choose smart phone $40 basic phone $30. For 10GB the cost is $100 not including other costs.
Both are very similar in pricing just a different way of saying it. Here are charts of what their prices are.