Why phone numbers do not start with one or zero

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Description of Dial

Q What are the features of the new type instrument?

A The dialing device at a subscriber's station consists of a disc with a movable top having a series of ten finger openings under which are placed the numerals 1 to 9 and under the tenth opening the numeral 0. All of the letters of the alphabet except Q and Z are associated in groups of three with the numerals 2 to 9 respectively. There are no letters associated with the numeral 1 because of the following conditions: A single movement of the receiver hook will cause a single impulse to be transmitted in the same manner as when the numeral 1 is dialed. As the hook may be accidentally moved while the receiver is being taken off or in some other way prior to the commencement of dialing the apparatus is so designed that a single impulse if it is the first one transmitted will be ineffective. It is necessary therefore that no call shall begin with a single impulse. As a letter is practically always the first character in a telephone number to be dialed no letter can be associated with the numeral 1 under the first finger opening. The word OPERATOR is associated under the tenth finger opening with the numeral 0 in the same manner that groups of three letters are associated with the other numerals. When it is desired to call the operator this finger opening is used and only one operation of the dial is required. There are no other calls beginning with the numeral 0 and the apparatus is so designed that the use of the tenth finger opening for dialing the numeral 0 immediately after any other operation of the dial will not result in the call being routed to an operator

From: Questions and Answers on Machine Switching System Panel Type