Cingular and other mobile providers got slapped with a patent lawsuit over "prepaid" accounts, which aren't anything more complex than purchasing a certain amount of cellphone minutes in advance and drawing from them over time, as opposed to going in for a regular per-month subscription allotment it's not too prevalent here in the States but is much bigger overseas.
FEMA's purchasing guidelines say the agency is supposed to line up contracts in advance so the details are already worked out when they need to place an order.
This allows players to advance at their own pace, with some users opting for frequent logins to burn energy bars and others purchasing packs and energy to play as they please.