Look at my other reply in this blog about saving data locally if your platform is iOS. Getting the file in the right directory was a little tricky.

The FileUtils.getFileUrl is only needed because I need to pull my mp3 file from the ios cache directory. Not sure about the difference with Android just yet. Assuming you can get a valid File reference though.

protected function loadSampleFromFile():void {
var fileUrl:String = FileUtils.getFileUrl(fileName);
if(_originalSample == null && fileUrl != null && fileUrl.length > 0 ) {
_originalSample = new SoundAsset();
_originalSample.addEventListener(Event.COMPLETE, loadFromFileComplete);

_originalSample.load(new URLRequest(fileUrl));
}

}

in the complete handler, after all of the error checking I did something like the following: where pos starts out as 0 which means from the beginning.

// 1/2 volume from beginning
var transform:SoundTransform = new SoundTransform(0.5, 0);
var _channelOriginalMP3:SoundChannel = _originalSample.play(pos, 1, transform);

Hope that helps