It's germane to remember that international communications were very different 78 years ago than today. Especially in wartime.
Trans-oceanic communications were largely by telegraph in those days, there was not really enough conductor cross section to support voice communication. (Most undersea cable is now used for data, satellites have taken up voice.)
So, it was pretty easy to "lock down" the oceanic cable juctions, and monitor telegraph hubs. International mail was also monitored and subject to review by both intel and counterintel agencies. Western Union would get, and send, encrypted and encoded messages, but logged the sources and destinations, which was reviewed by a number of US agencies.
Even diplomatic communications were watched, if not necessarily read.
Now, it was possible to have agents use various cut-outs, and linked drops. Which got complicated quickly. Like having to send something via the Paraguyan embassy to Spain, to be routed elsewhere. Which meant a lot of links, which kills speed.
We occasionally forget that Rural Electrification was not completed until the late 50s, that telephones were not universal until the 60s (and plenty of places on shared--aka "party"--lines until the 70s. "Named" interchanges (like "Belmont 5", e.g. BE5-nnnn) with a human operator were common until the late 60s. So, if you needed to call more than 20-25 miles away, you dialed an operator, who then connected you, manually, to a circuit. And, you were billed by the minute for using those lines (remember, it was American Telephone & Telegraph, they were using those same wires to run telegraph and telex communications when there were no voice messages online).
If you planted a person from 1942 in a modern house, they would be very confused. There would be no phone on the wall. No radio set to listen to. Very likely not a single book to read.
All while sittign right next to a cell phone, the remote for the tv, and a kindle/nook on the coffee table. And, heaven help our poor time traveler if the house has a "packet/cup" coffee maker.