The scenario would have been unimaginable for most people even a decade ago. A parent texts her son en route to picking him up from football practice: “Rning l8. Stck in traffic @ Nuneaton. Hungry?” As the message transmits it is screened by a computer that notes the keywords “traffic”, “Nuneaton” and “hungry” and matches them to its database of mobile-friendly advertising. At the same time, with the help of at least two satellites, it pinpoints the location of both mobile phones involved in the exchange and dispatches three restaurant suggestions to each, none more than a mile from the phone in question. It also lets them know where they can rent and download Traffic, starring Benicio del Toro. Mother and son end up enjoying chicken fajitas in a new Mexican café in Sutton Coldfield.

None of the technology required for this communications miracle is, in fact, new. Highly targeted advertising is already the lifeblood of many websites, and the combination of satellite tracking with the screening of mobile telephony content has been available in certain circumstances to law enforcement bodies for several years. This combination, as we report today, is now entering the commercial pipeline, and once available to consumers will constitute a new landmark in the erosion of the boundary between public and private; between how we define ourselves and how we let others define us by our choices.

The business case for mobile advertising of this sort is irresistible: extraordinary convenience for the consumer and almost intravenous access for advertisers to their target audiences’ desires. Customers may be offered lower prices or even free mobile services in return for allowing the content of their messages to be screened, and privacy concerns will be addressed, in principle, by an “opt-in” arrangement: customers receive advertisements only if they ask for them.

People will, indeed, opt in, and not just for cheaper mobile phone usage. The explosion of social networking and of sharing pictures and video on the internet has revealed a telling divide between those who remain deeply attached to traditional notions of privacy and those so unconcerned by them that they eagerly “lifecast” their entire existence via the web.

This divide is not necessarily generational. Millions of people, consciously or not, have decided that the benefits of increasingly promiscuous use of web and mobile-based technologies outweigh the potential risks. Those who provide or host the services they use are entitled to seek ways of increasing their revenue, and the screening message content may be one of those ways.

But the industry must tread extremely carefully. There is a fundamental difference between logging mobile phone call times, durations and destinations, as police have long been able to do, and “listening” to their content for commercial purposes, albeit with computers. It is not just paranoiacs who will find the concept alarming. There will be well-founded fears of vastly increased scope for the misuse of data by third parties, and of customers who refuse to “opt in” effectively subsidising those who do.

The chairman of Google, Eric Schmidt, wrote recently that the benefits of the digital revolution “have been so great that most people who remember the past would never want to go back”. It is up to people like him to keep it that way.