The iPhone corrects your typing as you go, but, until now, there hasn't been a method for performing an aggregate spell check on emails before they are sent.
Mike Schneider has released a new update to TouchType, an application that allows Mail.app to use the keyboard in landscape (vs. portrait) mode.
"I am really proud of the spell check feature. The results are very accurate and it works in 86 languages. I was planning to make spell check its own application, but when TouchType was unexpectedly approved by Apple two weeks ago, I decided to merge the two programs. The updated TouchType is still $0.99 and is a free update for existing users.
Other improvements include: support for all international characters and symbols, save functionality, enabling users to reuse text in email messages and create multiple email signatures, and general increased stability and bug fixes.