Twitter is the only social network that began life on a mobile phone -- which is why its 140-character limit corresponds exactly to the maximum length of a single text message. Unlike simple texting, though, Twitter is now fully integrated into the digital world, bringing images, Web links and real-time searches to your mobile phone in the form of billions of tweets.

Any phone with a mobile Web browser can visit the Twitter website, but it's all so much easier if you have an app or widget that plugs you directly into the Twitter-verse. There are hundreds of Twitter apps available for all the main smart phones, including iPhone, Android, Nokia, Windows Mobile and BlackBerry devices. Many of these apps are free, and even the most flexible cost just a couple of quid.

There's a Twitter app for every occasion. Use them to generate instant alerts when your friends tweet or you're mentioned; turn photos, videos or audio clips into tweets; share your GPS location or listening habits; or integrate smoothly with Facebook and other social networks. Some have cool features like letting you shake your phone to summon new updates.

Many non-smart phones come with home-screen widgets that happily work alongside Twitter. You might not get the full functionality of a dedicated Twitter app (retweets, direct messages, favourites and so on) but the widgets are great for posting updates to multiple sites simultaneously, and for keeping all your friends in one place.

Twitter is mostly about text so you'll want a good keyboard. Slide-out Qwerty keyboards will keep your fingers busy but don't write off touchscreens, which are fine for Twitter's short updates. Now that an increasing number of tweets contain shortened bit.ly Web links, look for a Twitter phone with a good-sized screen -- 76mm (3 inches) or more -- and decent resolution (320x240 pixels at the very least) for breezy browsing. While a 2G, GPRS or Edge phone will cope with basic browsing, 3G and Wi-Fi is sure to speed everything up.

No one uses Twitter for photo artwork, but the better your phone's on-board camera, the better your twitpics will look on followers' small screens. Autofocus is a real help and always go for an LED flash over higher-resolution capture.

If all that sounds rather expensive, don't worry. Because Twitter is rooted in paleolithic text technology, you can tweet from even the most ancient of mobiles. Just register your phone number with Twitter and you can then send tweets to a special short code (86444 for Vodafone, Orange, 3 and O2 customers) and receive tweets as ordinary text messages.

The CNET UK team of reviewers has chosen their favourite Twitter phones below, ranging from cheaper feature phones to full-fat smart phones.