The present disclosure provides a system and method for Session Initiation Protocol (SIP) user agent identification and efficient binding. In accordance with one example embodiment, there is provided a method for use on a Session Initiation Protocol (SIP) registration server for registering user agents, comprising: receiving a REGISTER message which includes a binding key; determining whether a prior binding associated with the binding key exists in a registration repository; and creating a new binding associated with the binding key and adding the new binding to the registration repository when no prior binding associated with the binding key exists in the registration repository.