Just two days after comments by Twitter investor Fred Wilson made third-party Twitter developers nervous about what the company might do, those fears have become reality: The company announced Friday that it has acquired Atebits, maker of Tweetie, one of the top Twitter apps for the iPhone (AAPL). According to a post by co-founder and CEO Evan Williams on the Twitter blog, the app will be renamed Twitter for iPhone and will now be free (previously, the pro version of Tweetie cost $2.99 to download). Developer Loren Brichter said on his blog that he is joining Twitter’s mobile team and will be developing Tweetie for the iPad.