Post #608810 by VampiressRN on Sun, Oct 2, 2011 9:12 PM

I remember having the 2 letters back in the 50's when I lived in San Diego...funny how our dials still have letters an now some businesses use the letters to help folks remember their number.

This might be what you are looking for...still from Wikipedia...

^ San Francisco and Oakland each had their own separate toll-switches, so calls had to be routed accordingly depending on the final destination. As the telephone equipment used at the time could only handle three-digit translation, the temporary use of area code 318 was required in order to distinguish between the two areas. Area code 318 was temporarily used to specify San Francisco and areas north of the Golden Gate, while calls with destinations in Oakland and the East Bay continued to use area code 415. When the electromechanical card-translator box became available sometime during 1952–53, 6-digit translation became possible and the use of area code 318 was no longer required. Area code 318 was reclaimed for future use and the entire San Francisco Bay Area returned to using area code 415.[1]