Bava Bathra 15b (original text here) says that there were seven prophets that primarily prophesied for gentiles, including Job and his four friends. Is the Talmud saying that the book of Job speaks ...
I don't think there were any gerim amongst the nevi'im, but would it have been possible?
When God addressed Moshe there was an accompanying miracle (and there's midrash about Avraham's case being special too), so it was pretty clear what was happening, but how did the other prophets come ...
Is there any suggestion in the scripture (even implicitly) that King David might have been also a Navi?