Have you seen the custom where people put their cell phones in a pile in the center of the table? First person to touch their phone pays for everyone.
I think the decline in manners is based on instant gratification - we have instant mail, instant texts, instant everything. People text instead of talking, email instead of sending a thank you note, and so on. And people definitely click "post" or "send" without thinking! The more that things are in writing, the less personal interaction there is - email and texting are communication without facial expressions and without voice inflections. So there's lots of room for misunderstanding.
I see kids in the movie theater at $11 a ticket, ignoring the movie and texting, often to the people they are sitting with. Crazy.
In my opinion, if you MUST take a call in a restaurant (or a store, or a checkout line, or a waiting room), you get up from the table and excuse yourself. You don't make others listen to your half of the conversation.