The phenomenal success of GSM carries with it extremely high expectations in terms of service quality and availability. However, the delivery of a flawless service is no mean feat, especially considering the complexity of handsets and networks. Much of the success of GSM in this respect lies in the detailing of the original specification. Essential operations, such as registration, require multiple transactions between the handset and the network. As calls proceed they need to communicate with one another to ensure that the call is maintained. Hand-off and other scenarios must be precisely defined and operate correctly. With UMTS now firmly entering the cellular picture, intersystem hand-off must be catered for so that handsets can revert to using 2G and 2.5G systems when no 3G network is available. The key to meeting subscriber expectations lies in the adoption of a thorough and vigorous conformance testing methodology for handsets to ensure that they operate properly on any network in any country. While the certification process may seem long and involved, it does ensure uniformity. Having already proven highly successful with GSM, a similar approach is being adopted for 3G UMTS or WCDMA, and there is no reason why a parallel degree of success should not follow in this new phase.