As has been reported and rumored for the last month or so, the much-hyped mobile messaging and community service Twitter is in the process of closing its $15 million round, and the investor is Spark Capital, we have confirmed through sources. Previous investor Union Square Ventures is also re-upping in this round, our sources say. Spark is the digital media-focused investment firm based in Boston, and has invested in companies such as Veoh, Kickapps, NextNewNetworks and others. In total, the company will have raised about $20 million after this round closes.

As we pointed out last week, the new round comes amidst a particularly bad stretch at the company, which has been suffering blackouts on a daily basis as of late. And of course, the business model part of it is still, well, a bit in the future, and more than anything, this new round is about buying the company time to figure out that part.

Dennis Miller, the General Partner at Spark Capital, is speaking next week at our EconAds seminar and will talk about online advertising deals...