And it's still a huge thing that shifted with the Internet too.
Prior to it, yes, there was international phone lines, but those were still expensive enough you might ignore them.
Before then, I'd say around start of the 90's in Europe, you did not represent yourself being in sync with someone, anyone abroad (but perhaps that started to become conceivable for people who could afford frequent international calls or travel).
And that conditioned how you perceived your own time, the time of others, the events here and over there, and the effort you took into communicating long distance, through letters.
I was recently a guest staying at an elderly woman's large house.
The room I slept in was full of junk, but what caught my eye were envelopes with stamps from the 1950s/1960s. The "From" name was the woman's late husband, and they were all from two African countries that were then part of the British Empire.
I had heard her talk about when her husband was working in Africa, but until I saw the big pile of letters I hadn't considered that this was the only way the young couple could keep in contact when someone's work required long periods of international travel.
No need to go as far as Africa. Basic landline telephones spread into poorer/more rural parts of Europe only in 1980s and 1990s. Until then it was either taking the bus to see people in person, or sending a letter....
E.g. quick search revealed this pamphlet from 1988 Spain, showing that ~30% of households did not at time yet have a telephone: https://www.telefonica.com/en/wp-content/uploads/sites/5/202...