Cox Digital Solutions has launched CDS Mobile, a new division to allow national advertisers to buy ads on local media mobile sites and national "vertical content" sites.

"Advertisers would potentially have the option of getting discounted rates from a cross-platform buy," MediaPost writes. "Cox will also offer publishers a suite of ad-serving technologies and tools for mobile, as it now does for Web advertising."

Leif Welch, who'll lead the new division, estimates Cox Digital’s mobile audience at about 90 million unique monthly visitors.

Cox Media Group itself owns 86 radio stations in 20 U.S. markets, as well as newspapers, television stations, and a cable channel. Cox mobile sites alone attracted 912 million page views in 2011, and mobile now accounts for 15%-30% of all digital inventory (according to Leif Welch, who'll lead CDS Mobile). The Cox Digital network (which extends beyond Cox-owned media) consists of over 2,600 total local newspaper, TV, and radio websites.

Mobile web and content traffoc has generally grown much faster than publishers' ability to monetize that audience. MediaPost reports that unsold mobile inventory is estimated at 80% across the industry -- and that's after last year's estimated 149% growth (to $1.6 billion) in U.S. mobile ad spending in 2011.

Read MediaPost's coverage here. The Cox Digital Solutions press release is here.