| http://www.w3.org/ns/prov#value | - Signal types include dual tone multi-frequency (DTMF), dial tone, voice prompt, voice...http://www.google.es/patents/US5636270?utm_source=gb-gplus-sharePatente US5636270 - Method of producing signals commonly used with telephones B???squeda avanzada de patentes N???mero de publicaci???nUS5636270 ATipo de publicaci???nConcesi???n N???mero de solicitudUS 08/430,179 Fecha de publicaci???n3 Jun 1997 F
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