It must have been Sokolov on the other end of that call. Sokolov had killed, or at least overcome, the men Jones had sent out to murder him, and ended up in possession of one of their phones, and hit the redial button. He had made some kind of a little speech to Jones. And he had mentioned Zula. That had to be it; that was the only time that Sokolov could ever have communicated with Jones.