“When you add cell phones into the mix, you can get extremely precise,” Feldman said. “Mobile phones have the potential to turn these [data] clusters into people.”

Among other things, mobile operators know about their users' musical tastes from their ringtone purchases and other taste-profile services such as Pandora and TheFilter.com.

But as mobile phones take on a greater role in interfacing with a range of applications, the amount of data tied clearly to the individual could mushroom. Motorola already demonstrates a feature that allows users to program their DVRs using their mobile phones. And TV players will be trying ever harder to get their hands on the handset: Zodigo, a new effort from Zodiac Interactive, has developed a mobile content search engine with the STB as the interface that tracks user choices and recommends similar mobile content, getting mobile phone numbers in return.

With all these data streams converging, how far can a telecom provider take this monetization? Most experts say it would be unwise to sell targeted advertising based on, for example, a user's interest in adult content. But beyond that common-sense case, what else is unacceptable? No one's really sure. Telecom carriers are urged to tread lightly, erring on the side of caution. The good news is that once carriers have decided where to draw the line, it's easy enough technologically to respect it: They simply don't track, or don't retain record of, visits to out-of-bounds Web addresses, and they don't offer such a category to advertisers.

Another no-no: using subscriber Web search terms to build profiles and sell TV ads. This would be tough to accomplish technologically, but more importantly, Feldman said, “If an operator tried to do that in North America, you'd see lawsuits fly.”

Actually, tracking URLs doesn't yield much useful information about users' interests, Feldman said. More precise information comes from user interactions within a given site, and those are known by the site owner, not the carrier. That's why site owners and carriers are likely to collaborate.

“It's to the benefit of both companies to share that information back and forth to build a better profile of that individual and sell it or use it in the future,” Feldman said.

Not all site owners will see it that way. Amazon.com, which has its own database of customer tastes and purchases, is likely to be protective of that data, Feldman said, while your a car manufacturer has more to gain. Going forward, companies such as Apple and Netflix will compete fiercely with telecom providers' subscriber data, and it's not clear yet in which cases partnerships will make sense.

The good news for privacy advocates: It's in the best interests of telecom providers to keep user information secret. It's just too valuable to give away. So instead what they'll sell to advertisers is access to anonymous but concisely defined groups of people. Advertisers will know what their audience is like but not who they are.

“The information has to be anonymized,” said Terri Richardson, group product manager for Microsoft TV. “I can't imagine a scenario where it wasn't.”

As well, marketers hoping to reach telecom subscribers believe that if those users are comfortable in their anonymity — because their service provider acts as a middle-man — those users might feel free to interact more with marketers. For example, users might sign up to receive a marketing e-mail relevant to their interests if they knew the transaction could occur without the marketer ever receiving the user's e-mail address.

“What [can be] exposed is some sort of ID that is not an absolute ID of that person but a token,” said Matt Johnston, CEO of Zodigo. “So I can have a local car dealer call you without ever seeing your phone number.”

To what extent consumers would appreciate that distinction is one piece of information that telecom providers don't yet have.