Unfortunately there is no sure -fire way to test the components you listed with out a functional LCD and Digitizer. The fact that the phone still rings is a good sign. It means that the phone is still on, the cellular modem is functional, and the speaker works. Given the fact that the speaker connects to the mainboard via the same flex cable that the microphone is on, there is a good chance that the mic still works.
My advice is to open up the device and take a look at the components. Look for any physical damage to the mainboard or flex cables. Also, check the battery and make sure it has not begun to swell. Sudden impact to the battery such as a car running over it may cause it to begin to swell up. In my experience the G2 is pretty resilient. So, if everything looks good on the inside, go ahead and get a new screen.