Various embodiments of the present technology allow multi-realm support at I/S-CSCF to IMS by the same I/S-CSCF nodes. Some embodiments allow for a registration message to be received from an IMS client. The registration message can be used to establish, through an Internet Protocol Multimedia Subsystem (IMS) core network, a service between a first endpoint associated with a first realm and a second endpoint associated with a second, different realm. The registration message can be translated so that the second endpoint believes the first endpoint is associated with the second realm before being transmitted to the second endpoint. Upon receiving a successful IMS registration message from the IMS core network, a binding can be created between the first endpoint and the second endpoint.