Friedman, Billings, Ramsey Group has announced plans to acquire a subprime mortgage lender and establish an MBS trading desk, initiatives that will extend and bolster the company’s current business strategy. FBR, based in Arlington, VA, is an investment banker built around an $11 billion portfolio of mostly agency ARM and hybrid ARM mortgage securities. The firm has been very active in underwriting a number of stock issues for niche mortgage originations. Its merchant banking investments…