Systems and methods for extending and re-using an IP multimedia subsystem (IMS) to extend the trust relationship from a closed group of customers of wireless service providers to users of other ecosystems (e.g., GMAIL, FACEBOOK, or YAHOO!) for IMS services are disclosed. Some embodiments include receiving a request from an initiating device to establish a service connection between the initiating device and an endpoint through an Internet Protocol Multimedia Subsystem (IMS) session. The request may include third-party domain credentials (e.g., maintained by a third-party domain) associated with an end-user. The third-party domain credentials can be extracted from the request. Communications with the third-party domain can be used to verify the third-party domain credentials. The IMS session can be established between the initiating device and the endpoint upon verification of the third-party domain credentials.