According to the Radio Advertising Bureau, off-air operations — largely comprised of online executions for radio stations — hit $1.68 billion in '07, up 10 percent from $1.52 billion the previous year.

That adds up to just seven percent of the radio industry's $21.3 billion in revenue in 2007, but it was the only business segment to show growth.

A report from Borrell Associates finds radio stations are still not cashing in efficiently on local advertisers. They received just 1.1 percent of the $8.5 billion spent on local online ads in 2007. Sales teams devoted to addressing local advertising has grown, but the problem may stem in advertisers' reluctance to spend on the medium. Most have their sights set on web 2.0 advertising.

Local online sales groups are also competing against Google, Yahoo and other portals for ad dollars, according to Borrell. Combined, portals received 43.7 percent of local spending last year.

Key to achieving the growth needed to offset off-line declines in radio are improved metrics. As television ad metrics are improved with internet techniques, radio must evolve in kind.