Twitter has taken a step closer to monetizing its uber-popular micro-blogging service. There is now a small, unobtrusive box for text advertisements on the user’s home page.

For now they’re just in-house ads, but a Google AdSense type of rotating links based on page content would be a very smart move on Twitter’s part.

The current ads link to either Twitter Search or the Twitter Widget.

Twitter has been floating a number of business models lately. A premium service and sponsored pages have also been rumored.

Twitter ads are not so much of a surprise really. The company has had display ads on Twitter Japan since the site launched a year ago.