There's a lot of American propaganda from WWII warning against the dangers of speaking about anything remotely related to a military operation, because the Japanese/Germans were listening and you'd get people killed. I.... Don't believe that. If you said loud enough for everyone to hear "on July 11th there will be an attack at Stuttgart" on a San Francisco rail car, and everyone on that bus told everyone they knew and so on, at no point along the grape vine would that reach The Japanese/Germans unless someone was actively selling information, and there couldn't have been that many infiltrators in America during the war, could there? I don't even see how wiretapping could be that big of an issue for the average John or Jane, who in hell is going to wiretap the entire civilian population of the US one switchboard at a time?

In the UK I can see it maybe more, but the only thing I would actually see as maybe a threat would be saying anything sensitive over the radio, which who would even be doing regularly enough to warrant telling them not to?