I don't think crossover songs always are just "picked up" by different genres. Sometimes, yes, but many times a label will send the song for adds with an impacting date in hopes of being picked up by stations. Program directors often look at iTunes and see how songs are selling and test them out to listeners in their market before adding them to rotation. They want to see how the song connects with the general public as well as with their own listeners. That's why stations have listener surveys and e-mail groups, etc. Or if they're interested in spinning a song they'll have those radio contests that pit one song against another and they'll ask people to call/tweet/e-mail with their opinion on which is better or they'll throw a poll on their website. Sometimes they take the winning song and test it against other songs for a few days and the winner is added to their rotation as they can see people like it.

Many times smaller stations will also check out the playlist of larger stations to see what they're playing and get ideas for new songs on their own station. So if say, Z100 picked up a song because the program director likes it and wants to spin it.. other stations could follow suit because they often want to emulate what larger stations are doing to get their success.

I hope that makes sense. But again I generally don't think songs just cross over without the label sending the song for adds. (And by that I mean it's almost like a suggestion to the stations and the adds date is the date they want stations to add the song to their rotation.) The stations will then listen to the song and consider it.

I hope I'm making sense. I'm not an expert by any means but I follow this stuff as best I can and this is what I've picked up on.

Thanks guys! I understand what all of you are saying, but let's look at an example like say for Pumped Up Kicks. How did it become so popular? It smashed on Alternative stations, but was it given an adds date and a push by record companies, or did Pop stations just decided to pick up on it because it was insanely catchy and followed the pop formula somewhat?

Thanks again