Popular iPhone app Tweetie 2 has received a major relaunch, and has become the first official Twitter app for the iPhone. Still dubbed version 3.0, with a nod to its Tweetie origins, the new app will hope to convince people to switch from rival apps like Echofon and TweetDeck. Tweetie was bought out by Twitter last month, so we all kind of knew this was coming.The Twitter app has been rolling out across the world all day, it seems New Zealand got it first, and it landed in the UK app store in the last hour or so.So what's all the fuss about? Well, it's got all the usual tweet app features such as your timeline, users information and browsing links within the app. The retweeting button is more prominent now.You can now search tweets, locate local tweets, see top tweets and browse through suggested tweeters.You don't even need a Twitter account to use the service, you can still see what's trending and what's happening in your vicinity, although you can sign up from the app's front page. You can even use the app with two different accounts if you tweet under more than one name.Give Twitter on the iPhone a go and let us know what you think, it's free after all. An improvement on Tweetie? Better than Echofon or TweetDeck? Or just a big flash in the pan? Let us know.