(with ease)
To start, bend the binding until you see it start to rip in a place. Then, straighten the binding out again, and squeeze very hard on the book, centered over the tiny tear. Clamp down hard, preventing the cover and pages from moving. This pressure is more important than bending it.
Once it's secured, bend it across that tiny tear, and the binding should just pop right open. This is really and truly is the "cheating" way. Too easy.
(or the "right" way, depending on how serious you take phonebook tearing)
You can hold one hand on the thigh, and rip towards the body. You can hold it to your chest and rip it in half, or you can keep the same grip and try to do the entire thing in one quick movement. With the size of the book shown, it should be a goal of yours to do so in one movement. If not, there's no real point in breaking such a small book over a 30 second time period. Unless your stuck in small town Georgia... Instead, try to examine the book casualy, and then with no change in facial expression, cleave it in one quick movement and look curiously at the two pieces. It gets a much better reaction than the "look how strong I am" routine. Then again, when doing a Major City's book, there's no way of avoiding the red face and grunting. Now you can use the "look how strong I am" technique.
Angle It: When you tear a book, think about tearing through the corner of the book at a 45 degree angle. This will make it so you are only tearing a small ammount of paper at first, and once the tear starts it gets easier. More paper is added as the initial tear gets to the thicker part of the book, but just follow the groove you started. Again, tear diagonaly, not straight into the book, unless of course, you are super-human.
Warning: Any phonebook, even a little phonebook left out in the Georgia humidity for a few years will make even the tiniest book all but impossible to tear. Watch out. I hate to admit this, but at parties, I pick up the phonebook when nobody is looking and test it, to see if it is crisp and can be torn. If it's limp and "soggy" I won't attempt it that evening if somebody just happens to ask me to tear it. This is why old time semi-legitimate strongmen baked their phonebooks and playing cards before ripping them.
Warning #2: Some books, either unique types, or just odd ones out of a batch, have a very thick, rubbery binding. So thick, that you can't tear through it. It will never split using the above technqiue, and needs to be twisted apart. This is another reason for "testing a book", to make sure you don't get caught with a rubber backed book while tearing for an audience.
Bending vs. Tearing: As an addicted bender, I see tearing as a type of bending. When you hold the pages tight, and tear, it's the same motion as a double-over-hand bend. When the pages are kept together with hand strength, the force of the "bend" will cause the pages to split instead of bend. Think of squeezing the book hard enough so that the paper is like steel, and then bend it and see that the paper can do nothing but easily tear open.
Technique: There are plenty of different techniqes that work for tearing a phone book. There are twists, snaps, bends and "S-shaping" that also work very well, but the above technique is the one that I feel works best.
Is it Safe?: My worst hand-strength training injury ever, was from tearing too many phone books. Even today, I still fell the slight twinge of pain in the 3rd and 4th fingers of my left hand. Don't over do it.
Paper Tearing: A fun way to practice is the paper-recycling bin. Grab hand fulls of used office paper and tear away. Also try to grab between 2 and 4 pieces and tear them, but then stack the two pieces, and tear those. Repeat until you can't tear anymore. This is my favorite way of judging progress in tearing.
Alan's Phonebook Tearing Page