The 3rd Generation Partnership Project (3GPP) R5 standards specified the use of Internet Protocol version 6 (IPv6) for the IP Multimedia Subsystem (IMS). However, early implementations of IMS are being introduced into the service architecture of existing access networks supporting Internet Protocol version 4 (IPv4)-only clients. As support for IPv6 clients is introduced into an established IMS IPv4 network, the transition to IPv6 must be handled gracefully and interoperability between IPv4 and IPv6 clients must be addressed. These issues have the potential to impact the access-independent nature of IMS specified by 3GPP. This paper illustrates a set of key technical challenges faced by both wireless and wireline service providers in deploying IMS services and offers a number of solutions for these challenges.