Cathy (waspfromipanema) had one of her songs on radio a few of years back, and it really was just a case of finding a suitable DJ/ show, and submitting the song. If there's a slot on your local radio schedule that you think may be appropriate for your style of music, then send it in. I think local and small stations are a better bet to begin with. If you get played it may make it more likely that you'll have a chance on larger stations.
I do know that the major labels use a 'plugger' to promote music to be added to playlists - this is basically someone who 'sells' the song to the station, although I'm not actually aware of any money changing hands (but it wouldn't surprise me).
You should do it though - it was a great feeling to hear it