How to access Facebook and Wikipedia for free, without wasting any data

To access Facebook Zero, all you have to do is add an actual 0 in front of the address (yes, only the mobile web view qualifies). In other words, simply go ahead and and type this into your phone's browser: 0.facebook.com. If the site at all loads, you'll likely see a black strip on the top of the page that says that your carrier is part of the program. If not, you'll be re-directed to an error page that makes it clear that your carrier hasn't enrolled into it.

But that's not all. Wikipedia Zero, as the name implies, is another such initiative hoping to bring data-free access to the world's largest repository of knowledge. Unlike Facebook, however, you don't necessarily need to do anything fancy to access it free of charge – the vast majority of participating carriers (full list here) will not charge you for browsing m.wikipedia.org anyway. In some cases, however, you may have to access zero.wikipedia.org to take advantage of the program. Like with Facebook Zero, a rectangular strip on the top will indicate if your carrier is participating, and an error page (at zero.wikipedia.org) will make it clear if it doesn't.

source: Facebook Zero, Wikipedia Zero