My guess is that in the coming years you will just see data charges on mobile phones, no voice, no text. It will all be considered "data". A 5 minute call will use a certain amount of data, a text message a certain amount of data.
The phone plan will be $X.00 for X Gigabytes of data, and you can use it however you like. There will be plan tiers for data, just as there are plan tiers for minutes today. It will become competitive, but by then there will be just a few major players. VZ and ATT will be the big dogs in the USA with a few minor players. T-Mobile is already likely to be absorbed by ATT, and I don't expect Sprint to survive much longer.