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The telephone numbering plan used for commercial service throughout North America is reviewed as an introduction to discussion of forthcoming modifications. Emphasis is placed on the procedures planned to increase the number of area codes and office codes beyond present limits. The structure of the worldwide numbering plan recently adopted by the CCITT is also described. Here attention focuses on the dialing sequence of interest to subscribers, namely, the access code, the country code, and the national number. Through discussion of the North American and worldwide numbering plans, the interacting and sometimes conflicting objectives of numbering are illustrated.