Developer A-Steroids has been waiting for microtransactions to become available on the iPhone for quite some time; previously making use of the backdoor method of selling 'point packs' as individual products on the App Store.
But now that firmware 3.1 is in full effect, the new premium version of Underground: SweetDeal will allow confection dealers to buy add-ons and goodies in-game.
The stumbling block for the satirical MMO (and many others, who'd previously been selling game credits as App Store products, presumably) is that Apple apparently doesn't allow developers to sell 'in-game credits exchangeable for virtual goods', which puts quite a dampener on the obvious use for MMO microtransactions.
To get around this, Underworld: SweetDeal simply allows you to buy items directly, for use whenever you need them. So you can now buy yourself a small protection pack, large carry space boost pack, super large combo packs and other items to make your illicit sugary sales easier.
The premium version of Underworld: SweetDeal costs 59p; a charge A-Steroids is obliged to put on the game for the privilege of using microtransactions. Hit the 'Buy It!' button to head on over to the App Store to check it out, and you can read more about the game's re-development on the official blog.