This may painfully silly to people with iPhones or who otherwise are very comfortable with iOS, but despite having my iPad for more than a year, I'm still figuring things out. For example, I've just figured out FaceTime and iMessage. So this post is really for people who 1) don't have an iPhone and 2) aren't used to working in iOS.
Basically, iMessage allows you to send SMSes to anyone in the world who also has an iPhone, iPad, etc. Similarly, FaceTime allows you to video chat with anyone in the world who also has an iPhone, iPad, etc. The trick, of course, is that they must have these things installed and configured to work. And of course, these are iOS-only tools (which is really kind of pain).
Sent from iPad, please excuse brevity & typos.