I grew up with rudimentary typing tools on older computers, but TabTyping aims to improve your typing on the iPhone's screen. The developer had to get creative when creating the app, so hit up the video for the story behind TabTyping's creation.
TabTyping is free and offers in-app purchases for additional lessons if you want to train your fingers to fly across that glass screen with unparalleled accuracy. TabTyping also provides a wealth of stats to track your progress, including your accuracy in certain parts of the keyboard on your screen.
At WWDC 2012 I spoke to Adam Wolf about TabTyping in this installment of Origin Stories.