Twitter has finally unraveled its official app for the iPhone, with the same interface of Tweetie 2.

Twitter bought out the Tweetie developer, Atebits, in April and is now offering the app for free to all iPhone users. The app was previously $US3.

Tweetie is widely considered the best iPhone app for Twitter, which is why Twitter decided to purchase the company rather than creating its own app from scratch, as it did for Android and BlackBerry.

A Gizmodo blogger said that other than a few small changes, the rebranded “Twitter for iPhone” is nearly the same as Tweetie 2. Twitter has changed the icon and start screen and added an improved search screen, but the functionality and format of the app will be very familiar to Tweetie users.

For users who already have Tweetie 2 on their iPhone, the new version is being offered as an update.

There is a large number of other Twitter apps offered on the iPhone, but the free release of Twitter for iPhone is likely to put them under pressure to innovate or risk becoming obsolete.