Millennial Media Files For IPO, Keeping Status As The Top Independent Mobile Ad Network

As the second-largest mobile ad network, and the top independent one, Millennial Media is the first to try to get an exit the old-fashioned way. It filed its S-1 documents today as the first step in going public, having nearly achieved profitability.

According to the filing, its revenues grew to nearly $70 million in the first nine months of 2011, a 138% increase over the same period in 2010; net losses, meanwhile, declined from $5.4 million to $417,000.

It’s competing for the same advertising clients and developer inventory providers as everyone else — but has 16.7% of the market, according to market research firm IDC, which is higher than everyone but Google-acquired Admob’s 23.8%. Apple, which bought another rival, Quattro, has 15.1%. The other big independent network is InMobi, which raised a $200 million round in September.

Overall, Baltimore-based Millennial is valuing itself at $305 million. It has taken on a total of $64.5 million in three rounds of venture backing, most recently a $27.5 million fourth round a year ago. Its investors include Bessemer Venture Partners, Columbia Capital, Charles River Ventures and New Enterprise Associates (which is about to add another IPO to its streak of public-market exits).