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Next month, Virgin Mobile USA will offer a new, prepaid smartphone plan that is really dozens of different potential plans rolled into one. It can be an emergency plan with just the bare minimum of minutes necessary to keep your phone number active. Or it could be a data-centric plan loaded up with gigabytes.

It could become a social messaging plan, allowing unlimited tweets(s twtr) and Facebook(s fb) posts, or it could turn your phone into a connected digital music player with no restrictions on audio streaming.

Virgin, which is owned by Sprint(s s), is calling the program Virgin Mobile Custom, and it will be available starting August 9 exclusively at Walmart(s wmt). The plan is limited to just three sub-$130 Android phones at launch: the ZTE Emblem and the LG Pulse and Unify. But Virgin aims to extend to other devices in the future, Sprint prepaid group President Dow Draper told me in an interview.

The high degree of customization comes from ItsOn, a company that specializes in next-generation carrier billing and policy. Some of you may already be familiar with ItsOn from its now defunct virtual operator Zact, which used the same customization tools in its plans. Zact was always intended as a showcase for ItsOn’s technology, and in that sense it accomplished its mission. Sprint recently signed a multi-year deal to license ItsOn’s service.

At the heart of Virgin Mobile Custom is an Android app, which can be used to set up a plan and tweak it at any time. According to Draper, a customer could select 1000 text messages initially, but in mid-billing cycle downgrade it to 500 messages. The customer would then be refunded for the difference, he said.

Voice minutes, messages and megabyte buckets can all be selected separately and they can be applied to individual phones or shared across five lines in a family plan. The app also comes with parental controls that can be used to finely tune the amount of talking, texting and surfing allowed on each phone.

The most interesting elements of Custom in my mind, however, are the app-specific add-ons. To tack on unlimited social networking – meaning apps like Facebook and Twitter wouldn’t count against you data plan – cost $15 a month. If you only Twitter regularly, you could buy a Twitter-specific add-on for $5 a month. Draper said other add-on choices include an unlimited music streaming option and an unlimited navigation option.

We’ve already seen T-Mobile go this route with its Music Freedom program, but these kind of toll-free zero-rated app plans are starting to pop up around the world. They’re an intriguing — though controversial — way for carriers to sell data in units more meaningful to the average consumer than the gigabyte.

Virgin will release more pricing details on the plan when the program launches next month.