Systems and methods are provided for supporting IPv4-IPv6 interworking of SIP messages in wireless networks and IMS networks. The interworking can be provided to smooth migration to an all-IPv6 IMS network by allowing the use and support of existing legacy IPv4 infrastructure. This functionality may be provided by a call session control function (CSCF) interposed between a user equipment (UE) and an IMS core network with interworking functionality or an interworking module. This device serves as a back-to-back user agent (B2BUA), allocates IP addresses from a pool, performs next-hop route protocol discovery, and maintains and stores information within the gateway as well as interworking and rewriting IP addresses within network messages, while proxying and maintaining sessions between the UE and the IMS core network. This allows for faster call setup, reduced capex/opex, improved debuggability, increased capacity and subscriber density by call processing distribution, and better user experience.