Twitter may have millions of active users, but many, many more millions don’t even have accounts. Which is what makes this latest news, big news. Twitter’s newest feature called “Fast Follow” uses a classic short code approach and makes it easy to follow anyone via SMS, even if you don’t have a Twitter account.

If you see a Twitter @username at a restaurant or store, on a billboard or on TV, or if you hear one mentioned on the radio, you can simply text “Follow [username]” to 40404 and you’ll start receiving all of that user’s updates via text message. The service can simply act as an SMS-based newsletter or text alert program. This would be a great way for bars and restaurants to simply and inexpensively promote daily deals or special promotions.

Certainly this could become annoying really quick if you follow someone who tweets all the time. But it looks like you’ll have some granular control over SMS messages you receive. Even more control if you have a Twitter account. But with SMS, you can turn text messages on or off by sending ‘on’ or ‘off’ to 40404.

You can follow @twittermobile to keep up with the latest mobile developments.

OTHER TWITTER UPDATES:  Twitter is launching an official Tweet Button for sharing articles on websites and counting how many times a URL has been shared, according to documents Mashable has obtained. The Tweet Button could launch as soon as this Thursday. Read>