[Ajedi32]

The problem with that methodology is that the cheapest plans in terms of cost/month are actually likely to be the most expensive in terms of cost/GB.

If a service provider offers a $20/month plan with 500 MB of data, their $40/month plan will almost certainly offer a lot more than 1000 MB. The cheapest plans are usually designed specifically for people who don't plan to use a significant amount of data.

[tobyjsullivan]

Alternatively you could argue that the cheapest plans are targeted at people who have the least money to spend on wireless data. It seems reasonable that these are the people who would be most sensitive to the unit cost of accessing a single website.