Comment by no_wizard

both iOS and Facetime are super slick and baked into the device. The end user doesn't even have to really know how to the app to use the feature as it were. It shows up on a contact as a button click.

Signal does not, even on Android. You have to deliberately use it.

That small friction isn't great when you're likely one of few people using it in day to day life of others.

FaceTime on the other hand, just works