eMarketer’s report shows that the Internet has already surpassed outdoor ad spending, and according to a recent report from Veronis Suhler Stevenson, online ads will displace television as the top one advertising medium by 2011.

However, radio is not a totally stagnant medium – the Internet's growth rate is feverish compared to radio’s. In fact, radio is expected to grow 1.5 percent in 2007. Total radio revenues increased 1 percent in the first quarter of 2007, according to the Radio Advertising Bureau. The Internet, however, which is expected to grow 22 percent in 2007.

Radio is the second medium to be passed by the Internet, while outdoor was first eclipsed in 2000.

However, the Internet may provide another opportunity for radio. eMarketer's Ben Macklin said that various kinds of Internet advertising will be "principal drivers for radio advertising growth" in the future.

In recent years, many radio broadcast and ad sales networks have been working to bulk up online sales capabilities. For example, in July, Katz Media Group purchased Net Radio Sales, which allows advertisers to deliver ads across a variety of audio and Web-based platforms. Ronning Lipset Radio announced its partnership with Corstarr to use its Adcor technology for delivering Internet radio ads. TargetSpot has also signed up many big radio broadcasters for its online service, so that advertisers can create and place streaming audio ads synced with banner displays on radio sites.