Box.net next month plans to open its online storage platform to third-party developers who want to offer services to Box.net's 1.2 million users.

Box.net calls its initiative OpenBox, and added services from a dozen partners this week. Those offerings range from online faxing of documents to photo and document editing.

The move is the latest example of a Web company looking to build more value into its offering by opening up the underlying user data to others who can extend the overall platform's services. Social network Facebook, for example, recently opened up its platform to developers, and Google has proposed a set of standards for developing applications across social networks. Analysts have said that another level of business opportunities will rise up once online companies move beyond enclosed offerings and start interacting across the Web.

Box.net on Dec. 5 plans to publish application-programming interfaces that other Web companies can use to program services into the platform. For those companies that already have their own APIs, Box.net is offering software tools that can be used to map a third party's data format with Box.net's.

If OpenBox takes off, it could help Box.net grow into a far bigger business by essentially becoming an open online file system for the Web. "We don't want to limit the functionality to what we have built in Box.net," Aaron Levie, chief executive of the company, told InformationWeek Thursday. "OpenBox is principally about customers being able to do more with their data."

Box.net subscribers would choose the services and pick the files they want to share. No service would have carte blanche access to anyone's data, Levie said. In addition, while any one can build a service for Box.net, it must be reviewed and approved before published. "We're taking security very, very seriously," Levie said.

Box.net is offering a lot of flexibility to developers in how they design their applications. The interface can be built so everything happens within Box.net, or a separate window can be launched for an operation such as photo editing. Services can be free, or carry a price tag. It's up to the originator.

Box.net is not asking others to pay for access to its users. The company is more focused on building a larger network, before considering revenue options. "This is not about business relationships and partnerships," Levie said. "This is about users taking their information anywhere they want on the Web."

In the future, premium services could be offered on a pay-to-play or subscription model, with payments handled through Box.net. "That's just under discussion right now," Levie said.

Companies offering services include Autodesk, Blogger, EchoSign, EFax, Myxer, Picnik, Scribd, Snipshot, ThinkFree, Twitter, Zazzle and Zoho.