A system for transmitting one or more communications in a telecommunications network, the system comprising: an application server configured to provide one or more services to at least two users of a telecommunications network, each user associated with at least one end user device configured to transmit and receive communications from the telecommunications network; a session border controller device in communication with the application server and the at least one end user device, wherein the session border controller device is divided to address each user; and a registrar module integrated into the session border controller device, the registrar module configured to: receive one or more Session Initiation Protocol based registration messages from that at least one end user device in communication with the session border controller device and register the at least one end user device with the telecommunications network, wherein the one or more Session Initiation Protocol based registration messages comprise an Internet Protocol address associated with the at least one end user device; and maintain a register having information comprising at least one entry associating the IP address with the at least one end user device, wherein the application server is configured to receive one or more SIP-based invite messages and, in response, the registrar module is configured to transmit one or more authentication messages to the at least one end user device, and wherein the application server is configured to receive from a said end user device that received a said authentication message verification of an end user's IP address and is configured to authenticate the verified end user's IP address with the information in the register. an application server configured to provide one or more services to at least two users of a telecommunications network, each user associated with at least one end user device configured to transmit and receive communications from the telecommunications network; a session border controller device in communication with the application server and the at least one end user device, wherein the session border controller device is divided to address each user; and a registrar module integrated into the session border controller device, the registrar module configured to: receive one or more Session Initiation Protocol based registration messages from that at least one end user device in communication with the session border controller device and register the at least one end user device with the telecommunications network, wherein the one or more Session Initiation Protocol based registration messages comprise an Internet Protocol address associated with the at least one end user device; and maintain a register having information comprising at least one entry associating the IP address with the at least one end user device, receive one or more Session Initiation Protocol based registration messages from that at least one end user device in communication with the session border controller device and register the at least one end user device with the telecommunications network, wherein the one or more Session Initiation Protocol based registration messages comprise an Internet Protocol address associated with the at least one end user device; and maintain a register having information comprising at least one entry associating the IP address with the at least one end user device, wherein the application server is configured to receive one or more SIP-based invite messages and, in response, the registrar module is configured to transmit one or more authentication messages to the at least one end user device, and wherein the application server is configured to receive from a said end user device that received a said authentication message verification of an end user's IP address and is configured to authenticate the verified end user's IP address with the information in the register.