Comment by drdaeman

Are we talking about momentarily checking if there's an important interruption and continuing with the conversation? If so, I'm confused as to why you possibly think it's unacceptable and rude.

I can see how this could be considered rude in a very formal setting, or when matters of high importance are discussed and uninterruptible focus is a must. But for most casual situations, I perceive glancing at incoming notification as normal. Assuming this happens reasonably infrequently, of course - that is, a glance in a while, not constant checking every other minute.