The social behaviour they generate is interesting on every front. For instance, there's this shopping mall close to the center of the city where I live. On the last floor, there are a bunch of restaurants, a small tobacco shop and the toilets. I go there fairly often, either for the tobacco or to hit the toilet.
Every restaurant has incredibly pushy promoters; the moment you set foot on that floor, these people immediately start handing you flyers, telling you about their restaurant, following you a couple of steps. I do my best to be polite with them; I know they're working on next to no payment, for imbecile bosses who think this is a good sales technique, so I'm never rude with them or anything. I just smile and say "Yeah, maybe some other time".
Sometimes, however, I'm just not in the mood for that. Long days, my own retarded boss, the incredible urge to go to the toilet (for some reason, there's no toilet around the place...), my hurry to get home and, until about a year ago, a lingering depression, simply mean I'm sometimes not up even to the little human interaction I need in order to politely refuse them.
So I just pop up my phone and pretend I'm reading a message or dialing a number. Suddenly, everyone's OK. No one would even dare disturb me. If I pretend I'm talking on the phone, the pushier ones will apologize for disturbing me, but will otherwise eagerly present me their offering. But if I have my eyes buried in it, it's like I'm suddenly invisible. One time, I even had to wait there for one of my friends to arrive, and stood there for at least five or ten minutes. No one even approached me as long as I kept my eyes down. I put the phone in my pocket for like five seconds because I thought I'd lost my wallet -- poof, two chicks appear to invite me to the marvelous restaurant that just opened and has a special offer just for me.