There's a subtle significance to the fact that almost all new forms of identity and communication are tied to individuals. From email to mobile phones to IM to social networking applications, a single person is the most frequent point of contact. Even businesses, which tend to have one central phone number, make it easier than ever to get to a direct extension for the party you intend to speak to.
Once, there was fairly frequent interaction with people who weren't your intended target of conversation. Speaking to a receptionist before getting to a business contact comes to mind, and its certainly an example that's not going away any time soon, but the more casual conversations are the ones that intrigue me. Your friend's younger sister who always ran to answer the phone first, the roommate of a person whom you spoke to frequently, your parents screening your phone calls when you were grounded; Those unexpected encounters with people often yielded extraordinary results.
I know a significant number of people who initiated business relationships with people they met while on hold as the phone was being passed, in contexts that we'd now call "loose ties". And that's not to mention romantic couples who met this way, resulting in everything from flings to marriages. I'd suspect all of us know at least one person whose parents met by accident because communication in the past was typically to a place before it was to a person. It's gradually gotten less centralized, of course; Few of us in the United States can remember party lines or going to a general store to get the mail.
So I lament the serendipity that's been lost. Many of the most interesting and exciting things that happen to us happen by chance, and now most of the time when I talk to someone, I do it by getting in touch with that specific person. There are of course the rare times when someone is using a computer that belongs to another person and that entry on my buddy list yields a surprise when I send a message. Or a few times I'll call a cell phone and it will have to get handed to its rightful owner before the conversation can begin. But those pass-through moments used to be commonplace, and used to result in the incidental creation of social capital.
We might not notice that those social intermediaries are gone, but I suspect when we recall in the future the anecdotes that result from them, the kids who are born today won't understand how a phone number used to belong to a family or a group of people or how, in the days before email, a message might pass under the wary gaze of a few unanticipated recipients. An "address" used to refer to a place, not a person.
Some would say this loss in accidental connectivity is more than made up for by the immediacy and efficiency of contemporary communication, and I wouldn't argue that point, for the most part. But I can't help but wonder if the delightful and frequently inspirational value that can come from a conversation that starts wtih "Hold on, I'll get him for you... By the way, who should I tell him is calling?" might be worth more than we realized, and that we might be well served by a moment's reflection when noting its passing.