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It just seems like most spies are lost by using their radios when they could chain a few calls through neutral countries would be safer.
Others can better elaborate or correct me on this but….
Spies used any number of devices to to contact their handlers, cohorts and others but phones were easy targets for listening in and were relatively easy to trace where the call came from. Every call went in through an exchange to be handled by a human operator and could be rerouted to a listening post add to that you were tied to a certain area with phones as they were not portable and if the lines were down you couldn’t contact anybody.
Radios were by far a better choice for as long as their batteries lasted you could transmit anywhere, messages were easily encoded and sent in short bursts and because every household had a family radio it was relatively easy to send coded messages over public airwaves to agents for them to do specific tasks.
This is in itself an expansive subject but I only just touched on the subject.
The main reason spies were caught using radios is because most spies used radios, not because radios were intrinsically insecure.
Phones are easily tapped (and stay tapped) - even if using codes. Radios can change frequencies, and as Dearth says, will run as long as batteries are available (or, if you have a number of safe houses, off the mains.). They don’t depend on the ‘host’ country’s phone system.
‘chaining’ a call is hard to arrange, and until satellites and digital switching, would actually draw attention of a wary adversary. After WW2, the NSA tapped every overesees call and did automatic testing of phone numbers, length of call and things like fax-machine calls, and even voice recognition (a field they quietly excelled at while the rest of us were still trying.) They do the same for emails that enter or leave (or even pass through) the US.
During WW2, spies could (and did) send messages via postal mail - for instance to and from prison camps. They were, of course, read by the enemy, so elaborate codes were used. The British had a whole division (MI-9) of intelligence for communicating with POWs and passing useful things like identity cards and radio parts to POWs in Germany.
Hope this helps, and welcome to the circus!
Great point, Philips Electronics managed to circumvent that by using a completely private hidden network. Ed Shames of the 101st used it from Tilburg. These prevented their communication to be tapped. (not sure if it worked a 100 percent.
Now instead of internet VPN it is also possible to buy connections via completely private cables. That way you avoid the internet. This is quite expensive so we don’t get bombarded here with this internet alternative.
Commucations in WW2 WAS remarkably advanced. E.g. Teletype conferences which were a very early version if Chats on teams (or AOL IRC etc),