FB (and social media in general) is the only thing I've found that enables me to organize going out for drinks with more than 2 people at once.
Also the only thing that lets me post "Hey, anyone wanna go out for ice cream tomorrow evening?" and actually having 5 people come. Three of which are completely new outside twitter/facebook.
It's really quite awesome.
Hell, I have very scatterbrained friends who are always busy with something. Without twitter, facebook and irc I'd never get to talk to them at all. Let alone be able to see them almost every other day like I do now.
And that's not even accounting for the fact that some of us tend to leave the country for months at a time, but still wanting to keep in touch.
Seriously though, how do you usefully and efficiently keep in touch with more than 1 person via telephone? I can't even imagine it working.
Oh and, word of advice from a "silly 24 year old". If looking at other people's lives makes you depressed, lead an awesomer life. Friends being better than you should be an encouragement to do better, not a depressor.