Can you let a phone call go unanswered, or a text unread for a while?

A person asked a Q on that Social Etiquette page I recently joined. She gets her hair cut and colored every few weeks, and sometimes she gets phone calls while she has crap in her hair. She can’t put it up to her ear, so she puts it on speaker, even though there are others in the room.
She asked if it was rude.
The answers were, without exception, a resounding, “Yes. It’s rude!”
I’ve been in the bathroom when someone will bang on the door, “Your phone is ringing!” like it’s some national emergency.

Can you ignore that call, let it go to voice mail, not respond to that text instantly?