This paper deals with the problems associated with full-duplex scrambled speech communications over analog two-wire telephone networks. The goal is not to describe particular scrambling systems or methods, but to analyze the situation in which the two users speak at the same time and each should hear the other. Current telephone scrambling devices preclude this feature. A general half-duplex scrambling model is described as a base to the discussion of pseudo- and true full-duplex communications. Finally, a novel true full-duplex scrambling architecture based on a paper by Cox and Tribolet [11] is presented.