IM's good if you're at your desk shooting the shit with your friends/coworkers. Unlike the phone, it's asynchronous, so you can reply when it's convenient. You also don't have to worry about eavesdroppers. It's better than SMS because a longer SMS ends up getting split over multiple messages and they can sometimes get stuck in the ether for a while, and you can use your keyboard instead of holding your phone and making it obvious that you're not working. It's better than e-mail because you don't want a gazillion one-sentence emails of BS going back and forth.

I generally keep email for "official" business or more thought-out messages to friends, Hangouts for more banal chit-chat, and I can always go back and search that if it turns into a more important conversation. SMS for the few weirdos who don't do Hangouts, and then voice is an absolute last resort. Real-time telecommunication just demands too much immediate attention- whomever I'm speaking to will say something that leads my mind to wander off and I'll miss a sentence or two, and then I can't go back and re-read what was said. Hate, hate, HATE calls!