You can do. There's no convention for crystal-ball speech. I wouldn't use quote marks unless they're speaking aloud, but that's just me. If they are speaking aloud, like on a telephone, then I'd probably just write it as normal.
I use italics without quotes for direct thought, and with quotes as remembered speech (so still in the mind of the POV, but an actual voice, albeit in the past). The former is a convention, the latter I picked up from Tolkien as a kid.
I also have written cases of POV characters being addressed by something possessing them, and in these cases I've started the line with an em-dash. It seems to work. Basically anything works if you're clear and consistent.