Twitter has just announced that it has acquired Atebits, the company behind the popular Tweetie iPhone app and Mac desktop application.

Tweetie's creator, Loren Brichter, will be joining the Twitter team as well. The app will be renamed "Twitter for iPhone" and be made free in the next few weeks. Twitter CEO Evan Williams explained the move in a blog post:

"We're thrilled to announce that we've entered into an agreement with Atebits (aka Loren Brichter) to acquire Tweetie, a leading iPhone Twitter client. Tweetie will be renamed Twitter for iPhone and made free (currently $2.99) in the iTunes AppStore in the coming weeks. Loren will become a key member of our mobile team that is already having huge impact with device makers and service providers around the world."

Twitter also specifically mentions that an official Twitter iPad app is indeed coming: "Developers, services, and publishers will be able to leverage the Twitter iPhone and iPad applications to create additional innovative tools and integrations for users," Williams said in today's announcement.

The move comes less than a week after a controversial blog post from Twitter investor Fred Wilson, Principal of Union Square Ventures. In it, Wilson explained that he is looking for Twitter apps to not fill holes in the Twitter platform (e.g. photo sharing, mobile apps) and instead focus on innovative products and "killer apps." The post caught the attention of developers, who feared that Twitter itself would begin competing with their applications.

It's uncertain what the acquisition of Tweetie means for unofficial Twitter mobile apps such as Echofon, TweetDeck, or Seesmic.