IDDD (International Direct Distance Dialing) A feature of the public switched telephone network (PSTN) that enables a subscriber to dial an international long-distance telephone number directly, i.e., without the intervention of an operator. Domestic DDD was introduced by the Bell System in 1951. DDD and IDDD are virtually ubiquitous today, although they are not available in some developing countries. See also appointment call, long distance, and PSTN. |