  We study some reduced free products of C*-algebras with amalgamations. We
give sufficient conditions for the positive cone of the K_0 group to be the
largest possible. We also give sufficient conditions for simplicity and
uniqueness of trace. We use the later result to give a necessary and sufficient
condition for simplicity and uniqueness of trace of the reduced C*-algebras of
the Baumslag-Solitar groups BS(m,n).
