In general, security evaluation of communication networks has always been of prime interest and in particular the ever increasing use of mobile phones in the last decade has led to keen interest in studying the possibility of hacking cellular networks. Security comes at an overhead in terms of either CPU cycles (computational overhead), bandwidth (communication overhead) and/or memory. While it is possible to theoretically design a system that is 100% secure, the operational overhead makes it uneconomical to deploy such a system in the real world. Often compromises are made in the real world implementation of a communication system and a trade-off is made between security and cost of operation of the communication system. In this paper we build a low cost GSM testbed to evaluate the security features in the commercially deployed 2G and 2.5G cellular networks in India.