I have always used SMS to send text messages to Twitter either when data coverage was limited, or when I was traveling without a smartphone. That is why I was surprised when I first heard people where unable to Tweet using Siri. All you have to do is enable tweeting via text messages from your iPhone.

1. Send a text to your Twitter code (40404 in the US) with the word “START”.
2. Twitter will reply and ask you for your username.
3. Send your username without any additional characters.
4. When Twitter asks for your password, carefully send your case-sensitive password without any additional characters.
5. Twitter will ask you to say “OK” if you want to use Twitter on your iPhone. Send “OK” to finish the activation process.
6. On your iPhone add Twitter as a contact, and add your Twitter code as the mobile phone number.
7. Ask Siri to send Twitter a text message. It’s that easy.

You may want to send an additional text message to Twitter with the comaand “OFF”. This will prevent Twitter from sending you notifcations over SMS. If you get stuck you can always tweet the SMS command “HELP”, or refer to this online list of Twitter SMS commands.