I have pretty strict rules for myself on pulling out my phone. If I am in a conversation I will not check it, period. If I am expecting a message that is urgent (how often does that happen though), I will excuse myself and step away. But if someone is in a group and there is a break in the interactivity and they check infrequently in a very low key way then that's cool by me.
Nothing worse than socializing with someone or a group of people, over a beer or whatever, and a good flow of conversation and laughs and then they just suddenly zone out for 3 minutes on their phone(s). That's a buzz kill man, and I am more than likely going to wrap it up and find something else to do.
Also, watched a fireworks show in Ottawa in August and the three teens sitting in front of us pretty much watched the whole thing through their phones recording it. How asinine is that?