Here is a little handy tip to make your device speak textual content with almost acceptable computer voice:
Go to Settings > General > Accessibility > Triple-click home to “Toggle VoiceOver” or “Ask” if you want to get a dialog asking wether to turn it On/Off (remember that tapping is done by double-tapping when voiceover is on).
Optionally go into Settings > General > Accessibility > Voiceover and set the “Speaking Rate” slider to around 20%, i found that speed to work best for me when reading papers.
Now go to your book or webpage or anything you want read and triple-click home and behold the machine start speaking your currently selected element,
Remember to turn voiceover off when you are done or else you will have to interact with the phone interface in a a whole different way (if by any chance you lock the device as i did you can unlock it by tapping the swipe bar to select it then tapping it again to unlock).
The major pitfalls besides the surprisingly hard to perform triple-tap home is that you have to select any text blocks you want read, and while this might be acceptable for pdf books where you can select a whole page in basically everything else you have to select individual paragraphs, even sentences, so do not expect a audiobook experience, and do not expect it to speak the contents of apps that do not have selectable text like WSJ, NYT etc (BBC/Reuters/AP work).
It is a shame Apple did not make it possible for this to be implemented as a book/content speaker with a consistent behavior and without relying on voiceover tricks, as it will even support reading in a lot of other languages than English, (for the full list see this for iPad and this for the other devices)
Voiceover is only available on iPhone 3GS, 4, iPad and 3rd generation iPod touch.