A Factor 3/2 Approximation for Generalized Steiner Tree Problem with   Distances One and Two
  We design a 3/2 approximation algorithm for the Generalized Steiner Tree problem (GST) in metrics with distances 1 and 2. This is the first polynomial time approximation algorithm for a wide class of non-geometric metric GST instances with approximation factor below 2. 
Piotr Berman, Marek Karpinski, Alex Zelikovsky