[David Atkatz]

Phone numbers became standardized at seven figures (letters or numbers) in 1931. Some cities had two-letter/four digit dialing before that, and some had three-letter/four digit dialing. A standard system of two-letter/five digit dialing was phased in thru the 1930s. The letters in all cases were the first letters of an exchange name -- MUrray Hill, SPring, COlumbus, UNiversity, INgersoll, TRiangle, HUBbard, COPley, KIRkland, etc. etc. etc.

The changeover to all-number dialing was very gradual, beginning in 1958 and continuing into the 1970s. The transition was smoothest in small towns, where there were generally only one or two local exchanges, and most difficult in large cities where there were many neighborhood exchanges and often emotional attachment to the exchange names. New York City held out the longest, with some of the old exchange names in use as late as 1978.

However, your photo's stamp is pre-Zip Code. And there is no postal zone number present either. (In NYC, postal zone numbers were incorporated into Zip Codes. I grew up in Bronx, 53, NY, which became Bronx, NY 10453.) The United States Post Office Department implemented postal zones for numerous large cities in 1943. So the stamp is pre-1943, even though the photo event was 1946. Still using an old stamp.