I tend to look at cell phones as something to be used in an emergency or to be reached if you are out and about and know you need to receive an important message. I agree with memason that one would be better texting in place of not talking to whoever they were with and it is to be kept at a minmum. My son has to take calls from work but he keeps these conversations to a minmum as he is respectful of who he is with. Like me.
I remember two episodes that are applicable:
1. A woman took her daughter to lunch and the daughter spent all her time on her cellphone. I would have ordered, eaten, paid the bill and left her to play with her phone.
2. I used to visit my brother and he became engrossed in the television show and stopped talking to me. If I wanted to watch television instead of talking to hm, I would have stayed home.
I think common sense and etiquette should prevale when socializing with other people instead of being engrossed in social media.
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"It doesn't cost "nuttin", to be nice". 
MOM
I just want to do the right thing! Uncle Joe, (my hero).