If you can set aside your doubts on that for a moment, simply consider that God could speak to every person as one... in spirit... within them... without the use of any other technological device at all.
A person not hearing does not mean that He is not speaking though. It is hard to hear the Spirit (of Truth: Christ)... if one is listening to a lie. The lies are loud and many. But I can only offer suggestions and share what happened with me. I can't actually answer for you. You would have to ask for yourself, and look within yourself.
You contradicted yourself. Earlier you stated that God speaks to every person, but by your own statement above your saying that gods voice is not going to get through to someone that is honest in working for Jesus or Gods (pick your form) interests but deceived. Let's take it a step further, aren't all Muslims and Chinese in the same boat by your criteria above? What good is speaking if it's not going to help 99% of earths population?
If God demands so much, wants to be acknowledged, and people to believe he exists then he really needs to clear some things up. Because there is no authority that can define "Right" for the people of the earth now.