Millennial Media last week celebrated momentum in the market by announcing several new partnerships and, for the first time, releasing some of its metrics.

Millennial Media said it added TV Guide, The Boston Herald, Goal.com, GoTV’s video service and The Washington Times to its roster of more than 1,200 sites participating in its ad networks.

With more than 1.94 billion U.S.-specific monthly ad impressions and more than 18 million unique mobile users in May, Millennial Media is the largest U.S. mobile ad networks operator, according to Paul Palmieri, president and CEO. AdMob gets more impressions globally, but “we have substantially more than anybody else in the U.S.,” he said.

In making the announcement, Millennial Media also took the opportunity to remind the industry that “open is not just for handsets.” One of the ways the online advertising industry took off is the ad serving technologies talked to one another. The same thing needs to happen in the mobile ad space, according to Palmieri. 

For example, a publisher might ask Millennial Media to insert an ad, but if it doesn’t have a paid ad to serve, it will send the request to another member of the ecosystem that can fill the bill. In the “all boats rise” scenario, the more eyeballs that can be delivered, the more publishers and carriers can make money.