Updates are displayed on the user's profile page and delivered to other users who have signed up to receive them. Senders can restrict delivery to those in their circle of friends (delivery to everyone being the default). Users can receive updates via the Twitter website, SMS, RSS, or through applications such as TwitterMobile, Tweetie, Twinkle, Twitterrific, Feedalizr, Facebook, and Twidget, a widget application. Four gateway numbers are currently available for SMS: short codes for the United States, Canada, and India, and a United Kingdom-based number for international use. Several third parties offer posting and receiving updates via email. Estimates of the number of daily users vary as the company does not release the number of active accounts. In November 2008, Jeremiah Owyang of Forrester Research estimated that Twitter had 4-5 million users. A February 2009 Compete.com blog entry ranks Twitter as the third largest social network (behind Facebook and MySpace), and puts the number of users at roughly 6 million and the number of monthly visitors at 55 million.
Twitter messages may be tagged using hashtags, a word or phrase prefixed with a #, such as #beer. This enables tweets on a specific subject to be found by simply searching for their common hashtag, provided that the user has tagged their tweet.