First things I'd check are the slider, the camera focus and flash, and the speakers and mic. If the mic isn't working, try to reboot, and if that doesn't work, reflash the firmware. Your device will still have a manufacturers warranty, or at least should. Even without a receipt, you can register the device online and they'll honor the warranty for a period of I believe a 10 day courtesy period. At least in the US it is that way.