Everything Mike says is right. However, I should add that in Germany - and the same probably goes for most Western countries - most radio stations are not even allowed to play records, which are not registered for copyright. In Germany, the song must be registered with the GEMA (I think it is ASCAP in the USA) and each individual recording needs an LC code. I do not know what the equivalent is in the US. This is so that the radio stations can report back to the relevant organisations, which pay royalties (for the songwriting and performance copyrights). One of the Mudcat solicitors - and there are a couple - will no doubt get back to this thread with clearer information.
The bad news is that even when you have done all this, the dice are loaded against you. In theory, commercial radio stations should have taken over where the pirate stations led off. Instead, I am afraid that the truth is better encapsulated in Alaska Mike's first paragraph. The corporations, who sponsor the "independent stations" insist on controlled playlists for their vassals. Moreover, the advertisers, whose income they are dependent on, insist on the same. So invariably most radio stations are obliged to play a high proportion of Madonna, Green Day and whatever is currently in the hit parade.
We Mudcatters are rather fond of the small minority of radio stations, which are not fettered by playlists. These brave people battle on against huge odds. Of course, competition for airplay there is very tough.
For some reason, a radio station is always more likely to listen to submissions from publishers or record companies. If you can get one interested, that is the best way to get access to the airwaves. Good luck!