Calling a subscriber would require giving his or her number to the hello girl.
City telephone networks came into being and every phone set was assigned a number.
In the 1910s automatic telephone switches started to supersede hello girls who made connections manually.
By the beginning of the First World War the USA had over 100 automatic telephone switches, Germany7, Great Britain2.
Mnemonic rules were in use in London and Paris until mid-1960s.
At first Americans adopted the LLL-NNNN format (three letters, four numerals).
Moscow saw the first automatic telephone switch installed not sooner than in 1924, and that one was in the Kremlin.
The city automatic telephone switch started operation in 1930.
For technical reasons no telephone number in the US started with 1.
Prior telephone models were directly connected to the operator or had a magneto (a rotating handle on the right hand side spinning which you also connected to the telephone girl). They were only installed in high-ranking officials offices (200 lines in the Kremlin and 20 lines in the Russian Council of Peoples Economy).
This sort of a telephone set was called vertushka (whizzer).
Afterwards the subscriber shall clearly pronounce the number to which he wishes to be connected.
How they call In todays Russia no telephones with Russian letters are produced.