What kaze no denwa means
Four syllables that outran their translation.
Kaze means wind. Denwa means telephone. No is the small possessive particle that links them, so the phrase reads literally as the wind's telephone, or phone of the wind. It is not a brand name and it was not coined by a committee. It is a description, and it happens to be exact.
Itaru Sasaki gave his booth that name because of a sentence he said about it, not the other way around: he wanted his thoughts carried on the wind, since an ordinary line could not carry them to a dead man. The man who built it named the object after what he needed it to do.
Why the English version is a compromise
Wind Phone is the name that stuck in English, and it works well enough. But translation flattens things it cannot help flattening. Denwa is not a neutral word for telephone the way the English word is neutral. It carries the specific, dated technology of a wired line, the kind of phone with a cord and a dial, which is exactly the object Sasaki used: an old black rotary handset, disconnected, sitting in a glass-paned booth. Wind Phone could describe anything. Kaze no denwa describes one booth on one hill.
That specificity is why the phrase kept showing up untranslated in film titles, documentary titles, and the novel written about it, even in English-language markets. Nobuhiro Suwa's 2020 film carries both names: Voices in the Wind in English release, Kaze no Denwa in the original. The stories told about the phone tend to keep the Japanese somewhere in the frame, as a kind of credit to where the idea started.
What a translation would have cost
A fully anglicised name, something like Grief Telephone or Memory Line, would have named the function and lost the object. Kaze no denwa keeps a trace of the sentence that produced it: the wind, specifically, as the thing doing the carrying. Not silence, not memory, not the universe in some vaguer sense. Wind, which moves, which you can feel on a hillside, which does not stay in one place any more than a voice does once it leaves your mouth.
There is also the plainer reason the phrase travelled: it is short, it is rhythmic, and it names a real place with a real history rather than a concept invented for marketing. Ōtsuchi is a specific town on a specific coast, and kaze no denwa is the specific name of the specific structure someone built there. Most translated ideas lose their proper nouns on the way into a new language. This one kept its noun and lost almost nothing else, which is a rare thing for a phrase to survive.
So when you see kaze no denwa written next to Wind Phone, it is not decoration and it is not an untranslated leftover somebody forgot to render. It is the more accurate of the two names, kept alive because English never quite found a replacement for it.
Say what you need to say. The line is connected to nothing: no one hears you, nothing is recorded, nothing is stored.