How to extract video’s background music and make it into cellphone ring?

I have a video file, and I love its background music very much and wish to use it as cellphone ring. But the problem is, I don’t know its name, so can’t download it directly. Now I hope to extract the background music and cut out part of it as cellphone ring. Could someone know which software can make it? By the way, my cellphone supports mp3 format as ring.
many thanks

You could try iMovie -> Advanced -> Extract Audio

OR

If you have GarageBand 3.0.4 from iLife '06, put the video into your Movies folder and select if from the Media Browser pane to the far right. Just drag it to the Track Window and it will create a video track and an audio track.

Just export the audio track to mp3.

my video file is swf, does iMovie support extracting audio from swf?