Well, this is a PG-13 movie, people. Chris Weitz clears the air:
"I would like to put everyone's mind at rest and let them know that the Volturi are not naked!" he wrote in a note released through the folks at Summit. "Jamie has what you might call a dry sense of humor, and almost managed to convince me--which is why he's such a good actor. Anyway, be assured that, even though we do want the look of the Volturi to be a bit of a surprise, they are as always--as in the book!--fully clothed."Source: Buddy TV
P.S. No offense taken, Jamie! What are you apologizing for? :-)