Is there a real connection between humans and jinn, and is it true that a jinn speaks through the tongue of the human it has "possessed"?

It has been established that jinn possess and afflict humans, as evidenced by Allah's saying: (Those who consume interest will not stand [on the Day of Resurrection] except as one stands who is being beaten by Satan into insanity.) Al-Baqarah/275. This is proof of jinn afflicting humans, and it is established by experience and observation. This occurs either for revenge or mischief. The best way to treat this is by reciting the Holy Quran over the afflicted person and performing ruqya (exorcism) with the reported supplications. As for what sorcerers do, it is forbidden, and treatment is only permissible through Quranic and Prophetic supplications.