MBS InvestorMBS InvestorFor MBS Mortgage Loans, either a Third Party MBS Investor for Lender-Arranged Sales, or the Multifamily Trading Desk. for an MBS Mortgage LoanMBS Mortgage LoanMortgage Loan purchased by Fannie Mae in exchange for an issued MBS backed by the Mortgage Loan. that is not the Multifamily Trading DeskMultifamily Trading DeskTeam that quotes interest rate pricing for a Mortgage Loan and can be contacted at (888) 889-1118. .