My home ISP gives me a certain number of megabit up and another down. My contract essentially says 60up/20down unlimited, which means that I can download as much as I want, subject to the limitation not to download more than 60 megabit a second.

We could use that as a template for 3g sales as well - granted we may have to specify the speed as 3g or 4g rather than a certain number of megabits - but ISPs hate that they are selling a commodity (which they shouldn't. Butter, toothpaste and oil are commodities but Procter and Gamble, Unilever and Saudi Arabia are all rich).