The situation in US is probably different, but in most european countries the telecommunications are ruled by monopolies (despite of proclaimed free competition) and certain services are simply too expensive or they are not available at all, while the profit of these companies is commonly higher than fair. People are frustrated and don't like these companies so they might like such ideas - the word "free" is undoubtedly appealing - however, I don't think it would get spread even if it would work (see below), as it is clumsy and impractical (although the technical concept (ultralow signalling) is interesting and it would make a very nice student work).

But the idea is not new at all, it is commonly used in a simpler form. "Just ring me once when you'll arrive", for example. The student just brought this idea into an outrageous extreme. On the other hand, I think telecom companies already know about this - for example, here the ringing of the phones is generally unrelated to the "ringback" tone at the caller so the caller has no control on the number of rings at the called. Even more, one of the mobile operators completely blocks the ringback coming from the other operator so you hear nothing until the called party picks up (or the call fails) - extremely annoying...

Jan Waclawek