When you're used to shortcut messages in text, this feature could be annoying.
I sometimes cringe at the messages I send, when they're way off on what I really meant to say.
I was a bit bummed when I first googled the answer to this problem. When I went to the first hit on google, this forum conversation told me that there was no way to turn this off. When I read the posts though, they were posted 2008.
Four years later, here's the solution for this problem:
How to turn off Auto-Complete
1. Go to SETTINGS
2. Go to GENERAL
3. Go to KEYBOARD
4. Then Switch Auto-Correction OFF
Check out Funny Texts caused by Auto-correct.
For more funny messages go to http://fyouautocorrect.com/