Did you know that you can insert accent marks and other symbols in any iPhone app that uses the iPhone's built-in onscreen keyboard? This is especially important when you're writing in a non-English language.
To see the array of accents and symbols available on the iPhone, simply hold down the letter or punctuation mark you want to add the accent to (some letters don't have accents, so they won't pop anything up). A row of accented versions of the letter will pop up.
To select the accented letter you want, keep holding your finger down and slide it across the screen. Remove your finger from the screen when the accented letter you want is highlighted.
Don't try sliding your finger across the accented letters. Instead, slide your finger in parallel to where you tapped to begin with (this may be under the pop-up menu).
The letters that have accents available are:
Punctuation marks that have alternate characters available:
(Thanks to reader Michael Louis for the tip on punctuation marks.)