Voices

Those people you try to avoid that are carrying on heated conversations with themselves, are really just time travelers. You see, in the future, when you are born instead of being given a social security number you get a phone number. It is yours for life. Then a crystal in grown inside you head as the connection to the network. If you don't pay your bill, you are forced to listen to advertising (cellular spam) whenever you are not using the phone.

So these poor souls are trying to avoid the advertising, even time travel won't protect them. Their only hope is to find some one to talk to forever to silence the advertising voices. Kind of a mobile tel hell.