Siri Dictation is another cool and very useful feature that is exclusive to iPhone 4S at the moment, but if you want to get it on your iPhone 4, iPhone 3GS, or iPod touch 4th generation right now then you can install a new tweak called Siri0us i.e available for free in the Cydia Store. Siri0us uses Nuance technology and converts voice into text for you.
Siri0us tweak works exactly like Siri dictation feature and adds a button on your keyboard by tapping on which you can dictate the text you want to enter through your voice. This tweak works quite seamlessly and efficiently converts voice into text with very few mistakes.
You can download Siri0us for free on your iPhone 4, iPhone 3GS, or iPod touch 4G by adding this repo in Cydia http://apt.if0rce.com
Here’s a demo video from Youtube in which you can see Siri0us in action.