Abstract: “Making the decision to migrate a user or service from a legacy network to a next generation network (NGN) requires thorough analysis. Despite the will and a clear necessity of telecom operators and service providers (SP) worldwide, many are still struggling with the migration process even after nearly five years and this can be attributed largely to the mentioned analysis aspect. New service delivery platforms (SDP) have necessitated the need to modernize or in some cases rebuild completely new operations support systems/business support systems (OSS/BSS). Mistakes have also been made in choosing an appropriate strategy for migration due to miscalculation in several key areas prior to migrating. Based on a task of moving users and services from legacy networks to IP multimedia subsystem (IMS) as well as inside the IMS, the current paper addresses the issue of making a solid migration decision, based on facts and proper analysis, concentrating mainly on the technical side of it. A high”

Keywords: analysis, IMS, migration process, migration phases, NGN.