AT&T partner Syntonic Wireless on Thursday unveiled the app store that will house applications and content eligible for the U.S. telco's toll-free data service.

Called the Sponsored Content Store, it will be available to AT&T customers with iOS or Android devices. It will roll out to other operating systems later this summer. As yet there are no details about exactly when it will go live and how many applications will be on offer.

"Syntonic is honoured to collaborate with AT&T and provide the solution that helps to bring sponsored data connectivity to millions of mobile customers," said Gary Greenbaum, co-founder and CEO of Syntonic Wireless, in a statement.

Announced in January, Sponsored Data gives over-the-top players the option to pay the data charges that AT&T customers would normally incur for accessing their services. It means subscribers can use participating OTT services without eating into their data allowance or being billed for the connectivity.

The move attracted controversy for two reasons.

Firstly, there is the argument that users are incentivised to access services provided by companies with the means and will to cover the data costs, rather than companies providing the best service, which impedes the ability of start-ups to compete effectively with established players.

Secondly, AT&T customers are already paying for what they consider an appropriate amount of data. By giving OTT players the option to cover the cost, AT&T is arguably charging two parties for the same data.

However, analyst firm Ovum praised Sponsored Data for encouraging greater mobile data consumption while extending the cost of that additional consumption to others besides the end user.

"AT&T is able to encourage more usage on its network, while the sponsoring company is able to promote and encourage the desired customer behaviour on their Website or interaction with their online or mobile service," said Ovum research analyst Sara Kaufman, in a research note earlier this year.