Music Application Code

Im looking to create an iPhone app. I would like the app to send sounds to a server in which puts the sounds together to make a song. So like recorded sound A starts the song, sound B starts at 10 seconds, then again at 20 seconds. Sound C starts at 40 seconds.

I can do the iPhone app portion of the coding. Im just not sure how to approach putting the sounds together to make a song?

Any ideas?