Selling additional products and services to a customer who already has your app can result in a steady revenue stream. Now, Google is looking to make that stream deeper for developers and publishers, by adding subscriptions to its existing in-app billing for apps obtained through its Google Play store.

The technology giant launched in-app billing for one-time offers on Google Play about a year ago, and the company said that the functionality is “extremely successful.”  In-app billing allows developers to gain revenue through try-and-buy offers, virtual goods, upgrades, and other one-off sales. It’s a key part of the “freemium” strategy, where apps are given away and extra features have prices. 

Google Handles the Rest

In fact, Google said that 23 of the 24 top-grossing apps in Google Play incorporate in-app billing, and the total revenue from in-app purchases exceeds that from initial purchases of apps. 

Now, monthly or annual subscriptions become another way to use in-app billing, through recurring and automated billing. Google said app providers need to set the price and the billing interval for the subscriptions, which are auto-renewing, and Google Play handles the rest. Google’s transaction fee of 30% is the same as for app purchases.

Subscriptions become part of Google’s existing user experience and its billing mechanism, with highlighting of such important items as price and billing interval, informing users of new charges, and sending emails to notify of each renewal. Google Play visitors can go to their My Apps at any time, to view or cancel any subscriptions.

Magazines, Game Levels

Subscription functionality, the company said, will now enable in-app magazine subscriptions, sales of bundled products or game levels, ongoing value-added services and more. There’s also the ability to provide access to the purchased subscriptions from developers’ Web sites, via an HTTP-based publisher API that allows outside servers to validate or cancel subscriptions.

One publisher, Glu Mobile, is using the new functionality to provide its customers with access to a single virtual currency across Glu’s popular Android game titles, such as Frontline Commando.

Google Play was created in March, as a rollup of the Android Market, Google Music, and the Google eBookstore. The move integrated Google’s Android app offerings, giving it a better platform to battle the highly integrated Apple iTunes. But, as with iTunes, the new subscription service also enlarges Google’s role in owning the customer relationship for all apps delivered through Google Play.