Play music from itunes over wifi on iphone (as soundbridge to Hi-FI)

Hey you all,

is there a tool around to play music over wifi on the iphone?

i have connected the iphone via the dockingstation to my hifi system.
so i can listen to internet streams and so on without using a cable from macbook to my hifi system....

but now i want to play all my music from itunes or another program on my iphone.


hope you know what i want...
i mean, the airport accesspoint can do so !?!?


kind regards
chris