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Over the past decade, wireline Service Providers (SP) have been looking for ways to evolve the existing PSTN network to Next Generation Network (NGN). The economics of the PSTN migration to NGN could not result in a positive business case for SPs. However, new market conditions are squeezing SPs' margins for traditional voice services in the PSTN. Meanwhile, recently standardized IP Multimedia Services (IMS) based solutions coupled with sensible migration approaches offer new opportunities for SPs to cost-effectively migrate the PSTN. This paper examines the SP's needs, the services architectures and platforms, the access technology alternatives, the inherent PSTN interworking requirements that need to be supported during the transition, and pending implementation challenges. It further leverages learnings from recent engagements with SPs globally to propose solutions that will help accelerate the migration of PSTN services to IMS. Finally, it concludes that maintaining the status quo has increasingly become cost-prohibitive for SPs, and that the industry has reached the tipping point for large scale migrations of the existing PSTN services to IMS.