Microtransactions, of course! However, creative director Matt Higby reassured us that the game won't be "pay-to-win." At Game Developers Conference last week, Higby promised that "anything that affects gameplay, such as grenades or medkits or implants that give you additional power within the game, will be exclusively unlocked via [in-game] resources."
Higby says that while upgrades will be free, PS2 will also offer "sidegrades," a term Higby repeatedly used during his presentation. A "sidegrade" would allow for a different play style, but isn't necessarily more powerful. To illustrate the concept, Higby talked about how one gun could fire less powerful ammo more rapidly, or more powerful ammo less frequently--the net damage would be about the same. "Things like sidegraded weapons that don't give you more power will be a split between Station Cash and in-game resources," Higby noted.
However, one part of the PlanetSide 2 in-game store won't accept in-game currency. "All the cosmetic stuff will be Station Cash-only," Higby added. Such is the price of vanity, no?