Speak and tweet. Now you can use a new Cydia tweak for jailbroken iPhone 4S that is called Sireet. You can use Siri to tweet through a free Cydia tweak that has been released recently. Only speak whatever you want to tweet and Sireet will translate your spoken words into text and post it using your twitter account.
It is required for Sireet to work that you have configured Twitter through Settings app on your iPhone 4S, and then open Siri to give a try to Sireet.