As operators start planning their 5G deployment, one important question that should not be overlooked is what should be done about existing 2G and 3G networks. The rationale for phasing out legacy networks is to ensure that spectrum is refarmed to the most efficient technology and by doing so reduce operating costs and optimise the cost base of the mobile network business. This is multi-faceted problem – aside from the business aspects such as competitive positioning and the implications on cost and revenues relating to service offerings, there are also wider policy issues such as the protection of consumers and key user groups, as well as the provision of public services. This Insight paper discusses some of these issues and the steps that need to be taken by mobile operators when phasing out legacy networks.