When I was a child, my mom told me that whispering to each other might be regarded as rude in some social circumstances. A dinner party, or a small social gathering of one kind or another.
(Not church, or funerals of course, but where people otherwise converse in a normal tone)

It made sense to me, so I have kept that as a principle of social manners-whispering is occasionally a rude thing to do. If you must speak privately, leave the room.

I regard texting in the same circumstances to be equally rude. My girlfriend has a friend who joins us occasionally for dinner, and she texts constantly. I never say anything, but I can’t help but regard her as sort of a douche.

I really do not think there is a firmly established social convention about this yet. But what do you think?