The iPhone doesn’t support Java officially (you would need to jailbreak it in order to do so). Steve Jobs doesn’t like Java. iPhone apps must be developed in Objective C which can interface with existing C code with no problems.
So you would have to use the AHNet C code and wrap a nice Cocoa interface around it.
Mike (Weller!)
EDIT: did I mention I’m an iphone developer now?
EDIT2: And apple are opening up the specs for using the phone’s usb port with custom hardware, but I’m not sure if getting better audio would be possible/worth it.