I too was having a real issue with low volume on my HTC One X. This was both front a back speakers and was getting to the point I couldn't use it.
Tried the toothbrush but it didn't help so I took to it with the back of a pin badge and the difference is shamazing! I wiggled the sharp end in each and every little hole. At first I was worried it might damage it but it didn't. It's like a new phone and at last I can hear the directions from the sat nav man and no more asking my firends to repeat them selves if there's a slight wind!