Yes, I think doing that in a 1:1 meeting can be seen as rude; just like going on a date, and your date is texting or answering calls in the middle of dinner!
But there are
definitely various types of meetings that involve, by nature, multitasking by the attendees, and it is actually for intent of making the meeting effective, not taking away from it. For example, meetings where the attendees are actually there as representatives for others, and those attendees need to take instructions from their clients or their principals (who are not there because in fact the attendees are their backups, or perhaps their representatives for other reasons) during the meeting. Everyone in the meeting is aware this is happening, and it is in fact expected, in order to keep things moving effectively. It really depends very much I think what sort of line of work and so on you are in, and what kind of meetings we are talking about.
And of course this is all very off topic so I shall move on now