Twitter

is a free microblogging service that allows users to send micro-text-based entries, called "tweets," of a maximum length of 140 characters. The sending of these messages can be performed either by the Twitter website, and via SMS (short message service) from a mobile phone, from instant messaging programs, or even from any third party applications, such as Twitterrific, Tweetie, Facebook, Twinkle, TweetDeck-Tweetboard or English. These updates are displayed in the user profile page, and are also immediately sent to other users who have chosen the option of receiving them. These users can restrict them to send these messages only to members of his circle of friends or allow access to all users, which is the default. Users can receive updates from the Twitter page, via instant messaging, SMS, RSS, and email. Receiving updates via SMS is not available in all countries and to request the service is necessary to send a confirmation code to an overseas number.