Putting your phone screen-up on the table is like ordering dessert -- one person does it and everyone else follows suit. Never mind that phones do not belong amidst tableware. As soon as a text pops up or a call comes through, everyone else at the table is trapped in conversational limbo while you have your own digital tete-a-tete.
If you must remain imminently reachable, simply make a big show out of it: "I'm so sorry to have to keep my phone out. Jess is supposed to get here soon, and I don't want to miss her."
The others will get the point. Either that, or they'll stick you with the bill. Don't worry, you'll likely be too distracted by Foursquare to notice.
Manners aside, here's the big danger with packing every spare moment with a cybercheck: Eventually, idle but perfectly interesting moments (sitting on a park bench, people-watching at a café) become excuses to busy yourself with your touch screen.
Remember that iconic New Yorker cover (see below) from last Halloween? Clever, sure. Terrifying, absolutely.
Soapbox, prepare to be climbed: Challenge yourself to go a week without using your data plan. Pretend you're on vacation overseas and can't afford the rate. Turn off Push and Fetch and all the other emphatic verbs that bring inane Facebook updates and new e-mails to your attention like a cat proudly dropping an especially fresh rodent at your feet. Stick to phone calls and texting and check everything else exclusively from a computer.
You'll see passersby, not pixels, when you're riding in a car; squirrels, not a screen, when you're waiting outside to meet a friend. And you'll make the liberating (albeit depressing) discovery that when you fire up your e-mail again, the world has continued to swivel without your immediate viewage of e-coupons from Suave and that cat video from Uncle Bob.
Those are best dealt with when you're at your desk and supposedly working anyway