[koolba]

It's not Indian specific either. I've seen it in a number of places throughout the world. It works anywhere that does not charge to receive calls (i.e. any sane place outside of the U.S.A.) as long as the caller doesn't get billed for cancelling.

You can get more than 1-bit of information as well if you sync the clock on your phone with the recipient. That gives you approximately 3.3 bits of information if you use the minute modula 10. This only works if you previously agree upon a meaning for values (Mod 0: Yes, Mod 5: No, etc).