Letters and a space are assigned to numeric keys of a pushphone. A desired numeral, letter or space is transmitted by depressing a corresponding numeric key a predetermined number of times, and thereafter a specific symbol key is depressed. At a reception side, a transmitted letter is detected in accordance...http://www.google.se/patents/US4658417?utm_source=gb-gplus-sharePatent US4658417 - Information transmission/reception system using pushphone and information reception apparatus
