Twitter, on their advertising blog:

We recently began testing Promoted Tweets and Promoted Accounts on iOS and Android devices to make it easier for brands to reach consumers anytime, even when they are on the go. As with the launch of Promoted Tweets in user timelines on Twitter.com, we started by showing them in the timeline only for those users already following the advertiser. Since we began testing three weeks ago, reactions have been positive. Starting today, we are expanding this test, enabling brands to target Promoted Tweets to mobile users that share similar interests with their existing followers.

Translation: Prepare for unsolicited tweets from advertisers.

A prediction: This “test” will either fail, or will result in an option to pay to remove these “Promoted Tweets”. There’s your business model right there.