Lock in of mobile number series with Telecom Service Providers has always been an impediment to ushering in healthy competition between the mobile carriers. While India has seen a rapid growth in the penetration of Telephony services, the same exponential growth is seen lacking when it comes to quality of service offered or openness of transaction with the large players. Though the initial enrolment of subscribers to specific carriers has an atmosphere of enthusiasm and a promise of quality around it, subsequently there is marked degradation in quality of service. Customers are discouraged to switch service providers as that would involve changing numbers and possibility of lost calls for the end user. Mobile Number Portability (MNP) is a technology that enables subscribers to switch their service providers while retaining their mobile numbers. Deceptively trivial in terms of nomenclature, the underlying technology that realizes this is quite complex and neatly integrated into the telephony infrastructure. The other significant aspect is the fact that MNP has reached the Indian shores in mid 2010. The TSP's have been mandated to adopt MNP and it has created lot of action and opportunity. The country as of now has 800 million mobile subscribers, as quoted by TRAI. Going by the Telecom Regulatory Authority of India (TRAI) guidelines, mobile users will be allowed to use the same mobile number even if providers use different mobile technologies like CDMA (code division multiple access) or GSM (Global System for Mobile Communications). This paper is thus looking into the pros and cons of MNP for Telecom Service Providers.