Millennial Media has become the latest to join the recent resurgence of tech IPOs. Or at least it has taken its first big step in that direction by filing its S-1 with the SEC, according to an email I just received from my contact there.

As the filing states, Millennial’s revenues were almost $70 million in the first nine months of 2011, a 138 percent year-over-year increase. It continues to operate at a loss, but net losses decreased from $5.4 million to $417,000 during the same period.

This is big but not suprising news. Millennial has been growing quickly as a major player in the fastest growing advertising medium on the planet. It’s the second-largest mobile ad network (16.7 percent market share, according to IDC) after AdMob (23.8 percent).

Even if you aren’t intimate with the mobile space, you may recognize Millennial for its monthly reports on mobile trends — as all media outlets out there (including us) are hungry for these data.

Notably, its past few reports have focused on the growth of location targeted mobile ads — one of many supporting points behind our our own forecast for location targeted mobile ad revenues.

Many pegged Millennial as the next acquisition target in the hot mobile ad network space, following Quattro (Apple) and AdMob (Google). That isn’t ruled out but is probably less likely now that it has indicated its intentions (not to mention inherently raising its acquisition price).

That “next in line” designation now likely falls on Jumptap or perhaps inMobi. And likely suitors could be Yahoo, Microsoft or perhaps looming giants entering the mobile realm such as Amazon or eBay (can you say shopping spree?). As they say, we shall see.

Meanwhile, Millennial is valuing itself at at $305 million. This comes after three rounds of venture funding that total $64.5 million.