I've seen it said to people here on numerous occasions that they are not highly educated if they believe in a god.
As others have noted, there is a negative correlation between education and a god belief, but there are highly educated theists, so the statement as written can't be correct.
I think that that education affects the way that they experience and live religion. There is a large and very visible distinction between our scientific theists on RF and the ones that have never learned critical thinking or the science. The latter typically allow too much religion into their lives, which is different from merely holding a god belief. By too much religion, I'm referring to the people willing to believe that gays and atheists are immoral, or who start thread after thread trying to prove the existence of God, or who disapprovingly believe that reason is an enemy to faith, or argue science that they don't understand, or believe that one should not engage with the world, or that the world is slated for destruction soon. You rarely see that kind of presence from the well educated.
There's a reason some denominations discourage university for their young adults, and why they want access to young kids in public schools. The see education as their enemy. They want to get to those kids before they develop critical thinking skills, and keep them that way by keeping them away from advanced formal education.
I've seen it said to some that claim that a god has spoken to them that they are possibility suffering of mental illness.
I assume that usually what they mean is that they have an intuition from time to time that they attribute to a deity, rather than hearing speech and words. That's not mental illness, that's just misunderstanding one's own mind. It's an ancient habit, going back to before the time when man understood what intelligence was, or that he had it and the beasts didn't, and didn't see himself as the source of new ideas. The ancient Greeks personified many mental functions. If one had a creative insight, it was a muse speaking to him, as creativity was the province of the gods. They misread their own minds and saw themselves under the influence of external agents. In Christianity, the struggle between the base urges and the higher self is described as a battle for the soul, with the Holy Spirit tugging one was and Satan the other, trying to lead a soul to perdition.
When I was a Christian, I had such an experience many times, misunderstanding the euphoria a gifted and charismatic preacher as the presence of the Holy Spirit. I don't think I was mentally ill. In fact, I was still rational enough to realize that that wasn't the Holy Spirit when I left that congregation, my first (I converted to Christianity there), after military discharge, and visited about a half dozen other congregations trying in vain to find the Spirit again. It was then that I realized that it was just misunderstanding my euphoric mental state, and assigning external agency to it.
Sam Harris said this:
"George Bush says he speaks to God every day, and Christians love him for it. If George Bush said he spoke to god through his hair dryer, they would think he was mad. I fail to see how the addition of a hair dryer makes it any more absurd."
I do. The hair dryer changes it from the typical misunderstanding of one's own silent mental states to a psychosis involving hallucinated audible voices. It implies hearing words through the device and speaking into it. That's mental illness.