AT&T is the country's fifth largest ad spender -- and now its using data gleaned from its own digital advertising to to help other marketers buying inventory through AT&T's AdWorks business.

The company is unveiling a new platform, called Blueprint, for targeted online, mobile and TV ads. However, the platform falls short of achieving what largely remains elusive for advertisers: a way to target one person or group of the same people across digital, mobile and traditional platforms. At the outset, there will be three Blueprint platforms: one for online, one for mobile and one for TV. Most notably, it will be using the intelligence it gathers from its own corporate digital ad efforts to inform the online Blueprint platform.

"We're both an ad network and an advertiser ... our ads show up in thousands of websites that go beyond our network. The nice thing about that is we can leverage that learning," said Maria Mandel Dunsche, head of marketing and media for AT&T's AdWorks. The company's own ads create 4 billion signals per month that it uses to identify audience segments and interest categories, said Ms. Mandel Dunsche.

AT&T overlays that ad-interaction data with search and other data derived from web interactions using AT&T WiFi hotspots. That information is then used to target audience segments in the AT&T network. "We're able to continuously update the audience segments," she said.

The ad platform was developed in-house by AT&T's Labs unit.

There are more than 70 million AT&T mobile subscribers that form the core of the mobile ad offering. The company uses anonymized subscriber ID information and segments users according to over 250 demographic, psychographic and contextual attributes to build audience segments for targeting in the AT&T mobile network, which encompasses mobile web and in-app inventory.

Combining its internal data with third party information, the company could hypothetically target mobile display or video ads to Hispanic moms with household incomes above $50,000 living in a rural area who often stream video, for example.

AT&T's television network scale is somewhat small. It's U-Verse digital TV network is composed of 4.8 million households and 12.7 million set-top boxes in the U.S. Aggregated viewership data is overlayed with third-party data to isolate segments of viewers who watch certain types of content. The company also will feed in inventory from Cox and other partners, said Ms. Mandel Dunsche.

AT&T can run campaigns targeting the same segment across all three platforms, but "what you can't do yet is be able to reach the same user across all channels," said Ms. Mandel Dunsche. "There's a number of obstacles: there's platform obstacles, privacy obstacles, data obstacles, measurement obstacles…what you're seeing is that we're laying the groundwork in order to have the capability to do that ."