Go into Settings, then General, then Accessibility, and finally turn Speak Selection to ON.
Use the slider to choose the speed of the speaking rate.
Open any email message and highlight the text you want read to you.
Tap on Speak
You can also use the Dictation feature of your iPhone 4S or iPad3 to record what you say into an email, and convert it to text. Create a new email, and then tap on the Microphone button on the keyboard. Begin speaking, and when
The Dictation feature will work just about anywhere on your iPhone or iPad where you have a keyboard. I use it all the time for texting.