You've got it all backwards.

The iPhone comes with a great number of built-in international keyboards. I will be discussing how to first turn on and then how to use the Czech keyboard. The great thing is that Apple made this easier than ever, and I hope they learn to make the Apple computer equivalents as easy to use (please see my previous article: Writing in Czech on your Mac). I don't want to waste your precious time, so here we go:

Installing

1. Quit any open application and proceed to the home screen by pushing the 'home' button on the front of your iPhone.
2. Click once on the Settings app.
3. Click once on the General settings button, at the top of the third group of buttons.
4. Scroll down to and click once on the Keyboard button in the middle of the fourth group of buttons.
5. Click once on the International Keyboards button near the bottom of the page.
6. All available languages will be presented alphabetically. Locate Czech and slide the toggle to the On position.
7. You are now done with the Settings app. You can quit and proceed to the home screen by pushing the 'home' button on the front of your iPhone.

Using

Now from any text entry screen where you are presented the keyboard, you should see a new key next to the space bar with a picture of a globe on it. Pressing this key acts as a toggle to go between your default keyboard (English I presume) and switching to our recently added Czech keyboard. Accents and the haček, can be achieved by pressing that key after the letter you want it above. Additionally you can hold down on a letter key to access a popup of alter keys that will include these and more illusive additions such as ů. Of special note is that once you install the Czech keyboard, the previous way of accessing the Czech characters will be available on the English keyboard. Sweet.

Good bye and good luck.