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 verisimilitudinous, but that's a heck of a word.) My initial guess is that it's somewhere after the 1920s but before the 1950s as 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.