A method of operating a bridge device to establish communication between an Internet Protocol, IP Multimedia Subsystem, IMS device and a non-IMS device (10, 20), comprising: receiving a request to instantiate as a proxy for the non-IMS device (10, 20) with an IMS network from a Call Session Control Function, CSCF in the IMS network; registering as the proxy for the non-IMS device (10, 20) with the CSCF; establishing a network layer level connection between the IMS device and the non-IMS device (10, 20), characterized in the method further comprising: using Session Description Protocol, SDP protocol messaging to negotiate a media type and/or format for communication with the non-IMS device (10, 20) responsive to establishing the network layer level connection, and then receiving an IMS format request to establish a transport layer level or above connection with the non-IMS device (10, 20) from the IMS device; sending a non-IMS format request to establish the transport layer level or above connection to the non-IMS device (10, 20) responsive to receiving the IMS format request to establish the transport layer level or above connection; and translating messages received from the IMS device from an IMS format to a non-IMS format for transmission to the non-IMS device (10, 20) and messages received from the non-IMS device (10, 20) from the non-IMS format to the IMS format for transmission to the IMS device responsive to establishing the transport layer level or above connection between the IMS device and the non-IMS device (10, 20). receiving a request to instantiate as a proxy for the non-IMS device (10, 20) with an IMS network from a Call Session Control Function, CSCF in the IMS network; registering as the proxy for the non-IMS device (10, 20) with the CSCF; establishing a network layer level connection between the IMS device and the non-IMS device (10, 20), characterized in the method further comprising: using Session Description Protocol, SDP protocol messaging to negotiate a media type and/or format for communication with the non-IMS device (10, 20) responsive to establishing the network layer level connection, and then receiving an IMS format request to establish a transport layer level or above connection with the non-IMS device (10, 20) from the IMS device; sending a non-IMS format request to establish the transport layer level or above connection to the non-IMS device (10, 20) responsive to receiving the IMS format request to establish the transport layer level or above connection; and translating messages received from the IMS device from an IMS format to a non-IMS format for transmission to the non-IMS device (10, 20) and messages received from the non-IMS device (10, 20) from the non-IMS format to the IMS format for transmission to the IMS device responsive to establishing the transport layer level or above connection between the IMS device and the non-IMS device (10, 20). using Session Description Protocol, SDP protocol messaging to negotiate a media type and/or format for communication with the non-IMS device (10, 20) responsive to establishing the network layer level connection, and then receiving an IMS format request to establish a transport layer level or above connection with the non-IMS device (10, 20) from the IMS device; sending a non-IMS format request to establish the transport layer level or above connection to the non-IMS device (10, 20) responsive to receiving the IMS format request to establish the transport layer level or above connection; and translating messages received from the IMS device from an IMS format to a non-IMS format for transmission to the non-IMS device (10, 20) and messages received from the non-IMS device (10, 20) from the non-IMS format to the IMS format for transmission to the IMS device responsive to establishing the transport layer level or above connection between the IMS device and the non-IMS device (10, 20).