I recently had friends over for a meal and the couple in question constantly checked their phones, posting on FB (they were quite open about it). Now, perhaps DH and I are terribly dull company but I was really put out that someone would behave so rudely.
If they had been checking on the babysitter or if DCs weren't settled etc I would have had no problem with it.
I don't think IABU.......but how on earth do you begin to address it? Do you call them out on it?