Updated*: MWC 2012 Nine operators have implemented an in-application API for the Wholesale Applications Community, so AJAX apps will soon be able to empty your pockets just like the competition can.
The new API – supported by AT&T, Deutsche Telecom and Telefonica among others – permits a WAC application to bill the user for in-application events such as upgrades or level unlocking. The same service is already offered by Google's Marketplace (on Android) and iTunes (for iOS Devices). But while those services bill events to the external account held by the marketplace – and ultimately to the credit card held by that marketplace – WAC applications will add transactions to the existing mobile-phone bill.
Not that this is unique: Google has done deals with some operators to link Marketplace accounts to mobile bills, and Nokia did a host of deals when it still had aspirations for the Ovi brand. But the WAC's premise is platform independence, and the idea is that in-application billing will remove the last incentive to develop platform-specific code.
The WAC then operates as a warehouse, providing a portfolio of applications from which app stores can select (and price) content as they wish. So users never buy apps from the WAC, they buy them from AT&T, Telefonica or whomever has signed up to flog WAC content (and pay the WAC margin).
Even when running on a supported handset, there are things a WAC application just can't do – such as running in the background while waiting for an event – so native development will always be necessary. Over on the official WAC Developer Forums, the 401 participants also report problems getting applications listed in operator stores, and realising that so few Android phones come with the necessary WAC runtime.
In-app billing might help operators take WAC more seriously, but in other markets it has not proved the money-spinner it was expected to be. The widely accepted perception was that games in particular would benefit hugely from the "Insert Coin To Continue" effect, but it's telling that the Mighty Eagle (an in-app purchase for Angry Birds) has been superseded in the latest version by The Mighty Dragon, who'll come and dispatch any number of egg-stealing pigs for free.
* The WAC collared your correspondent to point out that the billing APIs (and those alone) are also available to web pages, and so are not limited to the handful of phones supporting the rest of the WAC platform, which can only be a good thing.