I did not find Dvorak in iPod Touch's settings.
How can you have Dvorak in iPod Touch?
There's really no point to Dvorak on an iPhone. The supposed efficiency of the Dvorak layout assumes that you're able to use all 10 fingers. A smaller screen like that would need a completely different layout.
A layout optimized for the iPhone would need to take different things into account, because you're using thumbs rather than all your fingers. You'd want some balance of the most common letters on different sides of the screen, for example, to increase the chances that you go back and forth between hands. And you'd want each letter of common combinations likes "TH" on opposite sides. This is true for Dvorak as well, but in a different way. In this case, you might even want two instances of a few select letters so they can always be opposite of each other.
A layout optimized for a device of a similar size that used a stylus rather than your thumbs would be different still, because there's only one input. So then you'd want common combinations closer together, rather than opposite.
The point is that keyboard layouts were designed with specific goals in mind. QWERTY was actually designed to slow typists down to avoid mechanical issues on old typewriters. It's deliberately inefficient. Dvorak was conceived as a recognition that this no longer makes sense, and that the layout should now be intended to encourage speed instead. But the research behind it still focused on a typist using both hands on a full keyboard, and therefore it isn't necessarily good for a smart phone. You can probably find a way to get it on your phone, but that doesn't make it a good idea.
If you're willing to jailbreak it, you can run Cydia and install a Dvorak add-on for iKeyEx.
The accepted answer is excellent, but I'll add this last point: the iPhone's auto-correction algorithms depend on knowing the proximity of the "keys" to each other. For example, on a QWERTY keyboard, "Y" is next to "T", so when I type "YESY", the phone knows that I probably meant to type "TEST". It's important to recognize that not only does the phone have to know that "Y" is next to "T" (which is easy), but it also has to know, quickly, what other English words I might have meant, considering that both "U" and "T" are next to "Y", both "W" and "R" are next to "E", etc. This is hard.
In other words, the iPhone's English dictionary is almost certainly indexed and optimized based on the kinds of common mistakes made by QWERTY users. Rearrange the letters and, sure, the iPhone will know that in Dvorak, "Y" is next to "P", not "T" -- but its dictionary is probably not set up to quickly look up words that replace Y's with P's. For this reason, and considering how important auto-correct is to the smooth user-experience of the iPhone, I doubt Apple will enable Dvorak keyboards anytime in the near future. As a dedicated user of Dvorak keyboards, this bums me out, but I still love my iPhone.
Dvorak is a pretty niche thing and it's pretty unlikely to be a standard option for something as consumer driven as the iPhone.
It's also a keyboard layout designed to reduce fatigue with 10 finger typing which really isn't applicable to the iPhone/iPod Touch which means that they'd be developing it solely so people who already use Devorak know where the keys are slighly more intuitively (about 100,000 worldwide, most of whom won't have iPhones).
Anyway, no native support and I'd guess nothing coming in a hurry.
But you could look here: http://kasperowski.com/2008/05/iphone-dvorak-keyboard.html though it's a hack with some major issues.
From one dvorak user to another, embrace qwerty on the iPhone! The biggest disadvantage to qwerty on a regular keyboard is the far reaches, but on the iPhone this actually works to your advantage, and there is really no risk of CTS on a device like the iPhone.
My typing method is to use the first two fingers of my dominant hand, not the thumbs. One finger covers the keys on the left side, the other on the right. This, along with autocorrect, allows one to type fairly quickly with a low rate of mistakes. Fingers are much more nimble and accurate than the thumbs, especially with a touch device like the iPhone.
Granted, I think it would be somewhat advantageous to have dvorak since the vowels and common consonants are divided up this way, but it would also cause a lot more typos given the proximity of the frequently used letters. And while Apple has been good to dvorak users in the past, it is highly unlikely they will support this keyboard on the iPhone, as others noted here. So you should instead the qwerty layout on the device as a good thing, not a disadvantage!
The only method I've seen involves jailbreaking and hacking the Cyrillic keyboard, replacing it with the Dvorak layout. I tried it and there were issues so I abandoned it.
I am a Dvorak user and I have to disagree with people who don't want it on the iPhone. It's true that the gains of Dvorak on the touchscreen are negligent, but my iPhone is the last place in my life where I have to switch my mental context into Qwerty and I don't like it. In fact, one of the reasons I held off on buying a smartphone until the iPhone was I didn't want to be tied to a physical Qwerty keyboard on my mobile device. I assumed the dvorak support would be quick to follow. Doesn't seem like it's a priority. I guess I can't really blame them.