Here’s how to disable auto-correct once your iPhone has been updated to software version 2.2: Tap Settings Tap General Tap Keyboard Switch Auto-Correction to OFF
You can turn the auto-correct feature on or off any time you want, no need to restart your iPhone.
Even if you like the iPhone’s auto-correct feature, turning it of sometimes can be really handy if you are typing specialized terms that your iPhone keeps changing — or if your messages always include “duck” when that really isn’t the term you wanted.