It probably wasn't as a direct result of the recent announcement of Google's intended acquisition of AdMob, but that probably didn't hurt. Millennial Media just announced a new funding round of $16 million:

Today we announced the closing of our Series C round of financing.  The round was $16MM in growth capital, led by new investor, NEA.  Our existing investors, Columbia Capital, Charles River Ventures, and Bessemer Venture Partners also invested in the round of financing.  This capital is the second of two big deals in the industry in less than one week, and is a great indication of how vast the market for mobile media networks will be.

Baltimore-based Millennial has raised just over $37 million, including the $16 million, since it launched in 2006. According to Nielsen Millennial is the mobile ad network with the greatest reach. The company intends to expand its European efforts, among other uses of the new funding. 

We're now in a kind of race to greater scale among the various mobile networks. While there may be over 400 display "ad networks" online, the mobile universe will not support -- at least right now -- more than 10 or so competitors. That's because most display advertisers are going to want access to the largest audiences possible.