When people ring me why can't they hear me on my Samsung Galaxy ace?

People talk in my dreams all the time- I have had people record me sleeping and gesturing and talking about all sorts of subjects- I suppose it is just a matter of what goes on in your REM Sleep- maybe you're just not in a deep enough sleep to hear them or that you forget what you have heard by the time you wake up as your brain will tell you that nothing happened when in fact it did- each persons memories of their dreams are different - you should leave a recorder on all night that is voice activated- if you hear people talking in your sleep- you will answer them- then you will know for sure