Dave, my two MCs both hear voices, one of them from four distinct entities. I use italics for all such mind speech, using regular dialogue tags like said, asked, and replied as needed between the mind speakers. The MCs generally think to themselves using indirect thoughts in 3rd person past tense, although I do rarely switch to first person present tense to emphasize a thought, adding a thought tag if needed to be clear. With all due respect to Stephen King, I found that using special characters to surround mind speech is hard to read. It looks more like a page of html code than a novel.
If you're interested, have a look at chapter one ("Boys With a Destiny") of my book Into the Mind of God v3 to see the result. The scenes involving Joseph include God and Joseph's dead grandmother talking with him.
