In fact, in the past iOS versions (4.0-) the emoji keyboard is disabled outside Japan, for this reason to enable that you need to use an app (I used a free app, but someone make very money with a "emoji pro").
Now, in the last two versions (5.0+), the emoji keyboard is available for all users, for that reason you don't need to use an app to rack anymore.
I'm current use iOS 6 (this crap), and I can use emoji right the way.
A personal impression: Google is make the Android (software and hardware) better and better. In other way Apple is disappoint me day after day. I think to change to green robot, but I don't want to spend more $500 in my apps. The Apple jail me in the App Store. =(