An article from Dr Travis Bradberry which was posted on LinkedIn was shared with me in which he talks about "why successful never bring smartphones into meetings".
I must say, I couldn't agree more with the points he makes. As much as possible, I try to refrain from checking my mobile phone and using my laptop (or tablet) when I am in a meeting. I actually learned this the hard way earlier in my career when I was called out by the Managing Director of the company to stop using my phone while he was speaking. Yikes!
As a manager, I want to teach this lesson to my team as well. I want to help them avoid having the same embarrassing (and potentially harmful) situation wherein a Client or senior member of the company calls them out for using their phone. It doesn't matter if the call or SMS is urgent, or if you can multitask. The USC study quoted in the article actually validates this point of view as many of those surveyed over the age of 40 (to whom many Millennials will rely on for career advancement) think its inappropriate to take calls, answer texts/emails during a meeting and .
To me it boils down to respect. If one does not feel like the meeting is an important enough use of one's time, then I think the respectful thing to do is to just decline from attending. This is much more acceptable to me than attending and then spending the entire meeting fidgeting around using one's smart phone.