The "native" location data that Telcos have is not very precise - think of accuracy of a few city blocks. That is good enough precision for traditional subpoenas, but not for the kind of application the author described.
Also telcos only have data for their customers - this gets them access to competitors' customers.
With 4G the problem has been "what lane are you in?". One of the things that can be done with that data... If you can figure out what lane a user is in, you can target (visually) digital billboards to that lane, covering all lanes with different images/ads, through some weird refraction. I knew of a company that was working on that problem 8-10 years ago out of the South. No idea if they solved the problem.
A mind-bending digital info screen, developed in partnership with Misapplied Sciences and dubbed Parallel Reality, will debut in beta form on June 29 near the Delta Sky Club in Concourse A of the McNamara Terminal.
According to a news release, numerous passengers can look at the same screen at once, and each passenger will see personalized flight information that the other people looking at the screen will not see, because they'll be looking at their own personalized flight info.
The Parallel Reality display conveys the same sort of stuff you find on traditional airport screens—about departure times, gate numbers, baggage carousel locations, and so on—but you don't have to scan lists of data because the screen semi-magically shows you only what you're looking for, while up to 100 other people are simultaneously looking at the same screen semi-magically showing them what they're looking for.
Since at least 3g there is a capability to request the phone to report GPS location to the telco. There is even a capability to override disabled GPS before doing that, presumably reserved for law enforcement/search and rescue.
Also telcos only have data for their customers - this gets them access to competitors' customers.