My AT&T data use, by month. AT&T began to offer discounts for limited data plans, effective in the latest billing cycle.
The Freakonomics blog recently wondered if AT&T's switch to offering limited data plans for a discount to iPhone users might actually increase some people's usage, as they no longer feel as guilty about "hogging the network" as they did when everyone had unlimited plans (more on the details here).
I'm living proof. When the offer was announced, I noticed that my usage had always been well under the 2GB-a-month limit, which I could switch to and save a few bucks a month. I happily made the switch, and my usage the last month was almost twice as high as my average usage in recent months.
This is the same effect that occurred with the famous Israeli day care that began charging parents a fine if they picked up their children late. Suddenly, late pickups soared, as parents felt that they had morally balanced their books by paying the fine and thus were entitled to show up late.
(Side note: Isn't technology amazing? I used 500 MB of data over 3G signals last month, not to mention many more over Wi-Fi at home and at the office. I remember that my grandpa's first computer had an 80 MB hard drive.)