Just days after making its updated version of App World available to all, Research In Motion (RIM) acquired Cellmania, a company that offers back-end infrastructure for application stores. Current Cellmania customers include Sprint Nextel, AT&T, Boost, Virgin Mobile USA and Telstra.

Cellmania offers a platform that operators can use to accept applications from developers and sell them to users. The platform includes digital rights management and integration with a carrier's billing system.

RIM confirmed that it bought Cellmania but declined to comment further than to say that Cellmania is bringing its "expertise in application storefront development to the BlackBerry platform."

Cellmania has posted a brief note on its web page echoing that comment. Cellmania also said the company will continue to support current customers.

Last week RIM made App World 2.0, the updated version of its applications store, available to all users. It previously was open only by invitation. Updates to the store included allowing customers to buy apps with a credit card rather than exclusively through PayPal. The store also now lets developers sell applications for as little as $0.99. Previously, applications had to be priced at $2.99 or higher.

RIM has struggled to compete with new entrants such as Apple and Google that offer popular phones and large app stores. The recently released BlackBerry Torch was based on a new operating system and designed to turn RIM's fortunes. But some reports suggest that the Torch hasn't sold very well.

RIM has about 9,500 apps in App World. That compares with Apple's 225,000 and more than 65,000 in Android's store.