Both voice minutes and SMS tranches are for a mostly static demand though. I suspect that most users use about the same amount of voice minutes and SMS messages

Both voice minutes and SMS tranches are for a mostly static demand though. I suspect that most users use about the same amount of voice minutes and SMS messages as they did last year (at least if they are in a similar cell/landline situation from year to year). However, data demand isn't static, and it's going up. So I wouldn't expect to see data prices stay as stagnant as voice minute and SMS prices have, especially since that's the lucrative growth area cell networks have now.