The thing I hate the most is when I'm standing there having a conversation with a person and their cell phone goes off and they instantly put their hand up and take the call, expecting me to all of the sudden silence myself mid-sentence. They act as if it is well understood that the conversation between them and whoever is at the other end is automatically more important - The way I see it is they're ending a legitimate conversation to fiddle around with a talking plastic box. You'd think now that we have caller ID people would just look at who's calling and call them back at a more appropriate time or if it really is important they would say "excuse me I've got to take this, that's what I always do but most people try to silence a real live human being befor they even have their phone out. It's sad how many people have become puppets of their cell phones.
I have devised a solution to that which is working well. When people do that to me I ignore all hand gestures so they have to say something or walk further away to hear the phone call and usually when they say something it's usually a sharp "shhh". Either way at that point the conversation they were having with me is over and I won't pick it back up for at least a day. I tell them straight up that I would be willing to speak with them perhaps tomorrow or some other time when they don't have other such urgent things to do. I can barely keep myself from laughing when their phone call turns out to be some telemarketer or a dropped call or something. People I deal with now tend not to even look at their phones until a natural pause occurs in the conversation.