IPhone, why does my music stop when I go on some apps?

I have an iPhone 3GS and when I go on some appd my music stops, is there a way I can stop this?

Not that I know of. It stops because that app has sounds that the music would inter fear with.

Sometimes you can't avoid it with some apps. I have had it work before if I mute all of the sound in the app, close out, and then open it again. It will sometimes work, but not always.