Mobile ad network Millennial Media has launched something it's calling SMART, a monthly Scorecard for Mobile Advertising Reach and Targeting. The new brand-advertiser-focused SMART delivers key metrics gleaned from Millennial Media's ad networks, providing insight into reach, targeting, impressions and handsets.

All the SMART details come from actual traffic on the company's ad networks. Some facts and figures in the March SMART include:

* More than 10 billion impressions served in Q1 in the US, with 3.39 billion in March.

* Millennial's ad networks reach nearly 31 million out of the 56 million Nielsen-identified mobile Internet users.

* The top 20 handset models make up 43% of all mobile Web traffic on Millennial Media's networks.

* 58% of all campaigns used some form of geo-targeting.

You can get more info from Millennial Media's Web site. In the meantime, here are a couple charts from the report: