There's two things you should do if you want a serious shot at getting airplay...
#1: Join ASCAP or BMI
No radio station in the country (with a decent share of it's local market) will touch your stuff if it ain't registered through one of the musicians' unions.
Which leads me to....
#2: You have to get the song or CD to an independent promoter. The promoter is the guy who gives the radio stations 50 front-row tickets for the Aerosmith concert, which the station gives away in thier contests, in order to get some new band's CD played on that station.
Get it? It's a trade off. You scratch my back and I'll scratch yours. It's very rare (almost non-existant) for a non-union, non-promoted recording to ever get past the trash bin of any major radio station.
I'm not trying to discourage you, but this is reality.
You might want to try going to a college radio station first. The chances of getting airplay there are MUCH better, and if it's well-liked you might have a better shot at getting noticed by the "right people".
There's lots of bands that got thier start by appealing to the college crowd. It's worth a shot.
Otherwise, join one of the unions and seek out a reputable promoter who is willing to work hard to get you airplay. You have to be willing to accept a few setbacks, but keep plugging away. If you want it bad enough, and you have the talent, success will come.