用Context.getSystemService(Context.AUDIO_SERVICE)得到這個類的例項.

on   為true開啟喇叭擴音器；為false關閉喇叭擴音器.

若喇叭擴音器開著,返回true.反之,返回false.

	private AudioManager audioManager = 
			(AudioManager) this.getSystemService(Context.AUDIO_SERVICE);
	/**
	 * 揚聲器與聽筒切換
	 * @param isSpeakerphoneOn
	 */
	public void setSpeakerphoneOn(boolean isSpeakerphoneOn){
		audioManager.setSpeakerphoneOn(isSpeakerphoneOn);
		if(!isSpeakerphoneOn){
             audioManager.setMode(AudioManager.MODE_NORMAL);
		}
	}