Direct inward dialing is known as DID
Direct outward dialing is called DOD, or Direct Distance Dialing (DDD)
Direct inward dialing is known as DID
Direct-dialing of long-distance calls began on November 10, 1951, with customers in Teaneck and Englewood, New Jersey, able to direct-dial 11 cities in the United States.
Direct dialing just means that you dial the number yourself, without asking an operator to dial it for you.
Centrex features allowed direct inward dialing (DID) to a telephone number and direct outward dialing (DOD) from a number without operator intervention
The international and local area dialing codes would all be the same, but your long distance company of choice would have to provide you with their direct or operator assisted dialing protocols.
International direct dialing was phased in, beginning in the late 1960's and early 1970's.
The first direct-dialed long distance calls in the United States were in 1951. However, in the early days, the dialing procedure varied from place to place. Indeed, in many places, even until the early 1990's, you could dial a long distance call just by dialing the area code and number, without the '1' prefix.
Direct outward dialing
IDDC = International Direct Dialing Code.
DID means Direct Inward Dialing Feature in the PBX features in telecom.