Can I use Siri to update Twitter / Facebook?
Apple launched Siri beta with iOS 5 along with native Twitter integration. One thing that Siri can't do, however is update Twitter or Facebook directly. There is no built-in support for Siri to send updates to these social networking sites.
Luckily there is a simple workaround. Because Twitter can be updated via text message, Siri is capable of sending an update via text. See these instructions to configure your Facebook, Twitter or Google+ account to accept text message updates.