Tired of iPhone correcting your IM abbreviations and other words? Two ways to do it:

Retype it a few times

Tip: if you retype something twice, it'll stop autocorrecting it. E.g. if you try to send "np" as an SMS to someone, iPhone will autocorrect that to "no." So hit the delete key to erase the "corrected" word & retype it again. The iPhone will autocorrect it again, so delete it one more type & retype it, and it will stay. Third time's the charm. Plus, next time the iPhone won't autocorrect it at all, since it is now in the dictionary.

Note that sometimes I had to do the "third time's the charm" tactic twice before an unusual word would stay in the iPhone's dictionary & not get autocorrected anymore.

Click the Suggested Word Box

You can also click the "suggested word" box (anywhere in it, not just the X) to prevent the autocomplete and add the word to the dictionary.