What are the Voices?

[Onemario]

I try to look things up on the wiki, but I mostly get answers regarding the lore. That's fine and all, but I want a non-lore answer for what the voices are.

Furthermore, I've heard that SPEAK-AS-ONE and THEE-I-DARE are the only Voices to communicate using text visible after closing your eyes. How do the other Voices communicate?

[vindicar]

Voices are paid actors who basically join a random game session and start roleplaying with those present. They will ignore players with Enhanced Horror off, and won't join if the entire session has it off.
As you can guess, this means interactions with them are very, very rare as demand far outweights the supply.
They communicate using voicechat, with a bit of voicechanger thrown in. SAO and TID communicate using text, and you will see white "closing eye" symbol all over your screen, at least the first time they speak.
This is as much as I gathered from the community. I used to play with EH turned off so I never spoke to them.