With the news from Apple last month regarding in-app purchases for free iPhone apps, developers are surely thinking of ways to take advantage of that sort of payment scheme. Acclaimed game developer ngmoco is taking a stab at it with their latest first-person shooter, Eliminate.

The game is free to play, but to earn equipment upgrades and level up, players need to use “energy” from the game to earn credits. Players get an auto-renewable source of energy by default, but when that’s depleted they must either wait for it to recharge, or purchase more energy. You can still play the game without earning credits, but the more competitive players will certainly want to invest in them.

I suspect we’ll be seeing more attempts at this sort of monetization in the future. It’s an easy way to get your application in front of more eyes, and it’s a smart way to avoid the sticker shock of more expensive applications. It’s also particularly suited to games, because casual players can just keep playing for free, but also inch closer to becoming paying users the more they play.

We’ll have a full review of Eliminate in the near future. For now, view the trailer for the game below: