IMS networks and methods are disclosed for authenticating a communication device and a user of the communication device. When a communication device attempts to register with an IMS network, the IMS network receives a register message from the device that includes device authentication information, such as a public or private identifier for the device. The IMS network processes the device authentication information to authenticate the communication device. The IMS network also receives user authentication information from the device, such as a password. The IMS network processes the user authentication information to authenticate the user of the device. The device and the user are both authenticated by the IMS network. Authentication of the user may also occur when originating a session or terminating a session over the IMS network with the device.