Disclosed is a new method and compositions from the method consisting of block copolycarbonate/phosphonates that exhibit an excellent combination of flame resistance, hydrolytic stability, high Tg, low melt viscosity, low color and high toughness. Also disclosed are polymer mixtures or blends comprised of these block copolycarbonate/phosphonate compositions and commodity and engineering plastics and articles produced therefrom. Further disclosed are articles of manufacture produced from these materials, such as fibers, films, coated substrates, moldings, foams, adhesives and fiber-reinforced articles, or any combination thereof.