I'm deciding on my next campaign offering, and I'm dealing with this dilemma: although I prefer, and am best at, running games set in the near-present, one of my players has a mild antipathy toward modern settings. When pressed, she was able to narrow it down to "cars and phones" — the availability of commonplace instant communication and spontaneous long-distance travel. She's okay with having those things available to the rich or well-connected, or as public utilities — the telephone in the hotel lobby, or in your home, but not a pay phone on every corner.
For my own comfort and hers, I'm looking to see how late I can push a 20th Century setting and still have the absence of ubiquitous telephony and automobile access be "realistic." (Or versmilitudinous, but that's a heck of a word.) My initial guess is that it's somewhere after the 1920s but before the 1950s; car culture and the interstate highway system come into effect after that. Moreover, I'd appreciate resources that show the transitions in these technologies — how did people cope with the introduction of these resources — so I can more accurately depict the way that traditional adventuring difficulties like isolation and long travel times diminish and disappear.