It was just yesterday that Apple announced they would allow free apps to enable in-app purchases, and developers are already jumping on the "get the app for free, buy the content later" business model as quickly as they can. ngmoco came out swinging, as Touch Arcade reports, with both a free intro version of Rolando 2 out for purchase, with later chapters of the game as add-ons. They've also been working on a shooter called Eliminate, and we're now told that title will be free as well, with extra content to buy later.

The creators of Urban Rivals, an app that is based on a virtual trading card game, have let us know that they too plan to go the free-with-microtransactions model as soon as their app is released, and though we haven't actually heard from Tapulous, Andrew Lacy told us outright that the only reason Tap Tap Revenge 3 had a 99 cent price tag on it was because of Apple's limitation, so we'll expect that app to go free as soon as it can.

Clearly, there's a drive for this model on the developer side, but the question will be just how much this echoes with consumers -- certainly the "download a trial, buy more later" model has worked well on other platforms, so we can expect it to work here on the App Store as well. But on the other hand, just as when the App Store first opened for business, it's a very "wild west" moment -- everybody and their brother is offering up in-app transactions, and they're all of varying prices and quality.

My guess is that we'll see a few "hits" -- a few free apps that everybody buys content for (Tap Tap Revenge 3 is a good guess; considering that because you know most of those songs, there's much less guessing on what the quality of the transactions will give you). At the same time, there will likely be apps that everyone agrees aren't worth the in-app purchase (it's the old story of "horse armor" when Xbox Live started doing microtransactions). Until we find a good balance, where quality meets price, odds are that it'll be tough for consumers to know just what's worth it, and thus tough for developers to convince them that their content is.

Tapulous COO Andrew Lacy sat down to talk with us just before the release of the software, both about how he thinks consumers will react to the new business model, and what's next for Tapulous and this series that has come so far already. Tap Tap Revenge 3 should be in the App Store very soon -- it's available for 99 cents, with extra music packs at six songs for $2.99, or two songs for 99 cents.