如果音频已在iPhone上播放，则听不到通知声音

using sdk 4.1 . The wav file that is played when a push notification arrives on the device plays fine when no audio is being played on the iphone but if there is audio being played it is not heard. Is there any way of getting it to play superimposed on the existing audio , even if it sounds quieter that is ok.using sdk 4.1 . The wav file that is played whe