I can't remember what is was called but there is also a package for jailbroken phones that adds a "voice" option when you highlight any text. I use it for long emails while on the road.
Of course, this is of no use if you're not jailbroken though.
I use an app called Speak it Text to Speech for reading stuff to me. You have to copy and paste the text but its easy enough to do and gets the job done.