n essence, the technology involves inserting a data stream into a TV or radio broadcast and receiving it in a way that does not interfere with the primary audio-visual signal. The data can be combined with the audiovisual signal or sent along as a separate part of the spectrum, then transmitted to a special receiver tuned to capture the bits.
The economics seem irresistible: Transmissions can reach millions of people as easily as one, and provide steadily increasing margins as the viewership grows. Internet and cellular phone technologies, by contrast, create additional costs for every new connection.
Could be an interesting technology to look at for updates in remote/rural areas.