TELECOM Digest Editor noted in reply on this topic:
When Philadelphia converted from 3L to 2L-N, the third dial pull was definitely NOT the third letter in almost all cases. That is, WAVerly (928) became WAverly 4 (924) and WAverly 7 (927), WALnut (925) became WAlnut 2 (922), BARing (227) became BAring 2 (222), BALdwin (225) became BALdwin 9 (229). In other words, in effect almost everyone got a new phone number. I suspect they did that intentionally to make the change clear.
I forgot the year Philadelphia changed, but it was very close to or even within WW II. At that time the Bell System absorbed the competing Keystone Telephone company (which served only business customers with flat rate service and some outlying towns) and had to create more lines from them.
In 1943, Philadelphia cut over to the first #4 Crossbar for toll switching. I'm surprised this happened during the war, but perhaps it happened because of the war and the need for faster switching and efficiency. Someday I'll have to search newspapers if there's any mention. There is no index of those years and it requires a manual search through the microfilm. The above 3L to 2L merited only a very brief newspaper mention the day after and nothing the day before, to my surprise.
(To show how priorities changed, the introduction of new el cars in
1960 was full front page major news, with numerous side bar articles. Suppliers of car components had ads in the paper. In contrast, a 1982 replacement of subway cars had far less coverage, still front page, but much smaller and no sidebars. New buses get no coverage today but in 1954 got a full page ad by the transit company.) [TELECOM Digest Editor's Note: In Chicago, the third 'L' nearly always became the first 'N' _except_ in a few cases from pre-dialing days when there was a conflict. Then, some other first 'N' was chosen. As certain exchanges filled up with customers but geography dictated retaining the same name (such was the case with GRAceland-2 and a few years later GRaceland-7; Graceland Cemetery on the north side of town is a major place; quite a historical spot.) But generally they very cleverly worked around those problems, as with MIChigan-2 and MIDway-3 and MItchell-6. (MIChigan is both the lake and the street downtown while MIDway Plaisance is the main thoroughfare criss-crossing the University of Chicago. PAT]