$1 - (2% fee + 30c card fee) leaves them with very little. I wonder how they get around the credit card fees. Supposedly Apple would want their 30% cut as well.
Say they get 30c per user.
You get 1T traffic for $1, so 300G for 30c. That's roughly 40Gbytes per year or 100Mbytes per day. As long as people are on expensive mobile plans, there won't be more data.