While SOE don't seem ready to reveal the exact business model for Planetside 2, they have said that the game will have a "free component" and also a cash shop. Speaking to Planetside Universe Smedley said:
There will be a cash shop for the game however the goal is not to sell power. For example we would sell things like customization because we would like there to be a massive amount of ways to customize your characters. So people could recognize you or your outfit out of a group. We will not sell a more powerful gun or vehicle.
Quite what this means isn't clear, although it sounds promising. I am hoping it will mean that we get free reserves to keep the numbers up and a premium option for the more dedicated players.