[mark-r]

In the story I remember, the parallel universe is discovered when they agree to meet at an important landmark building in New York - but they never meet, because in her universe the original building was destroyed by a bomb that hit New York and the building was rebuilt in a new location.

[ctchocula]

"Out of this World" (1964) by Alfred Bester. Here's a stackoverflow post: https://scifi.stackexchange.com/questions/251779/phone-calls...