I found it odd, that the victim, or someone else, had a cell phone on and was talking to the victim's girlfriend while this was going on?
I thought it too odd to say it, and I really didn't care at first, (and I may be the 7019th person to suggest this) but I think if there is any audio of the shooting, it is probably fake.
There is audio of police recordings from neighbors. In one of them, the calls for help and the gunshot are audible in the background.
http://mp3.911dispatch.com.s3.amazonaws.com/sanford_zimmerman_911.mp3