If you’re not comfortable touch typing, Keyboard Challenge, a simple game that teaches you the position of each key of the keyboard, could be of assistance.
The game is simple, you just drag and drop all the keys into their slots in the least number of clicks possible.
These free apps / websites will help you understand how fast you can type using the touch screen of your iPhone (or iPod Touch). Plus there are resources / shortcuts to help increase your overall typing speed using the virtual keyboard of your iPhone.