Mobile number portability allows a mobile subscriber to switch operators without changing his/her phone number. This article describes and analyzes mobile number portability routing mechanisms and their implementation costs. We first describe the Signaling Relay Function (SRF)-based solution for call related and non-call related routing. Then we describe the Intelligent Network (IN)-based solution for call related routing. Cost recovery issues for number portability are discussed in this article from a technical perspective. We note that rules for cost recovery also depend on business and regulatory factors that vary from country to country.