The window for going public is open for today’s most attractive technology and digital media companies, even if Wall Street has been relatively cool to new tech issues.

Yesterday, mobile ad network operator Millennial Media announced that it is joining the IPO fray, filing its S-1 in the U.S. to go public.

According to that S-1, the company hasn’t yet generated a profit but is
growing rapidly, seeing revenues of $70m through the first three
quarters of 2011, up from $6.2m total in 2008.

On the surface, that growth, although impressive, wouldn’t appear to
make Millennial Media an appealing IPO prospect. After all, other tech
companies that have gone public recently had greater revenues and higher
rates of growth, but the market hasn’t necessarily treated them very
well following their debuts.

Millennial Media, of course, is in a market few argue is going away any
time soon, and that could make all the difference.

The company is
serving 40bn mobile ads each month, making it one of the largest mobile
ad networks in terms of ads served — perhaps even the biggest by some
counts.

Thanks to its size, it’s a hard network for marketers to pass
up. Even if they’re intrigued by Apple and iAd, for instance, marketers currently
have to buy from the largest players like Millennial Media to reach big
audiences across multiple mobile platforms.

With the mobile advertising market growing rapidly, and some making
bullish (if not crazy) predictions about where it could be in just a few
short years, there’s a decent chance Millennial Media could be more
intriguing to Wall Street than companies like Groupon and Zynga, even if
it isn’t yet profitable.