856 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



but the Z is never used in a central office code), hence any office code 

 will always avoid a 1 or a in the first two places. The digits 1 and 

 can therefore be used in area codes to distinguish these from office codes. 

 It is not practical to use them as initial digits of area codes since custo- 

 mers dial to reach operators and the local dial equipment is arranged to 

 ignore an initial 1 for technical reasons. A 1 or in the second place, 

 however, can be employed in an area code without conflicting with an}^ 

 central office codes or interfering with any existing practices. Accord- 

 ingly the area codes will consist of three digits with either a 1 or a as 

 the middle digit, 516, 201, etc. A few codes of this type are now in use, 

 leaving a practical total of 152 of these area codes available as compared 

 to approximately 90 assigned to our present numbering plan areas. This 

 will provide a comfortable spare for additional future numbering plan 

 areas or possibly for reaching overseas points which may later be in- 

 corporated into the toll dialing network. 



As shown in Fig. 1, states and provinces such as Montana or Alberta 

 which are contained in a single numbering plan area will have area 

 codes with a as the middle digit to distinguish them from areas in 

 divided states such as Texas where the middle digit will be a 1. This is 

 to enable toll operators to differentiate between the two classifications 

 of areas. On calls to single area states the operators will always know that 

 every call to the state in question uses the one area code, whereas on 

 calls to subdivided states additional information will be rec^uired to de- 

 termine which of the several area codes should be employed to reach the 

 particular destination. It is proposed to show on the operator position 

 bulletin the codes of all single area states and the codes of all frequently 

 called cities in multi-area states. The area codes of the less frequently 

 called places in the multi-area will be obtained from a routing operator. 



Within each numbering plan area each of the 500 or fewer offices 

 are to be given a three-digit office code which will be different from that 

 of any other office code in that same area. Ultimately each central office 

 will be given a 2-5 type of number consisting of an office name and five 

 numerical digits, such as LOcust 4-5678, illustrated for Philadelphia. 

 In the larger cities customers will dial seven digits, LO 4-5678, on local 

 calls to numbers in the same exchange. In many of the smaller places 

 the customers on local calls will dial only the numerical digits, the office 

 name being employed for toll dialing purposes only. 



Considering the thousands of central offices which now have numbers 

 other than the 2-5 type and the fact that to change existing numbering 

 systems is a difficult and often costly procedure, it will be a number of 

 years before this ultimate objective is realized. As a practical measure, 



