Here is how to tweet from Siri completely hands-free. By the way, I wrote this post by dictating to Siri (which is #eduawesome).
Update Sept. 20: If you have iOS 6, Siri now allows you to Tweet. Twitter is deeply integrated into the new operation system. (If you’re running iOS 5, you may read on.)
Go to Twitter.com settings, and click Mobile. Enter your mobile number and Activate Phone. Copy the phone number, and add that number to a new contact. Call that contact Twitter.
Now from Siri you can say, “Send a message to Twitter,” and it will automatically post to Twitter for you. Stoked.
Here’s a few extra tips. Siri understands the word hashtag, so feel free to use it. You can add your number here. If Twitter is being difficult, here’s a support article about adding your number to Twitter. You can perform some fancy commands, like RT and unfollow, via SMS. Here are the fancy SMS commands. As always, be sure to double check what Siri has dictated before you send it.