On first blush, it would seem that Siri is unable to send tweets or update your Facebook status. But with a little maneuvering, she’s putty in your social-media-loving hands, making it that much easier for you to stay connected.
To get started with Twitter, text “start” to 40404 – the code varies depending on your country, so if you’re outside the US, check here for other country codes. You’ll get a response within a few seconds asking for your Twitter login. Once you’ve logged in, add 40404 as a contact in your Address Book. Name the contact entry something obvious, such as "Twitter." This way, when you tell Siri to "send a text message to Twitter," she’ll recognize it as a contact.
The same goes for Facebook. Text “hello” to 32665 (check here for other country codes). Click the link in the return message and add 32665 as a "Facebook" contact.
Once you’ve got everything set up, all you have to do is tell Siri to “send a text to Twitter” or “send a text to Facebook,” and you can update your statuses on the go.