Great news for those who are terrible at typing emails in the iPhone’s portrait format: Mike Schneider’s brand new TouchType App (App Store; $0.99) allows for message composition in landscape mode.
So far, TouchType only works with iPhone’s mail App, but an update is in the works that will also allow for compatability with Apple Notes, as well as the ability to save snippets of texts as email signatures.
As for SMS messaging, the developer mentions that he has yet to crack that code…but never say never!
Accessories & Apps: Beta Testers Wanted
iOS Firmware/IPSW Download Guide
Legacy iTunes Download Archive
App Store Top Charts
iPhone and Android Resale Value Charts
USA iPhone Carrier Plans Compared
Complete iPhone Jailbreaking Guide 
Complete iPhone Specification Matrix 
There’s another app that does this too .. and it also has the extra feature of automatically saving drafts to finish later. It’s called Wide Email ($0.99) .. here’s the iTunes link:
http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=289274499&mt=8