1. A method in an IP Multimedia Subsystem Gateway for enabling a legacy host, attached to a local network, to discover a service provided by a remote server, comprising the steps of: subscribing to an IP Multimedia Subsystem presence service; receiving presence information published by the presence service, said presence information including at least one Globally Routable User agent Uniform Resource Identifier (URI); receiving a service discovery message sent by said legacy host; searching said presence information to identify a requested service and an associated Globally Routable User agent URI; and, sending a response to said legacy host including a local network address of the Gateway, whilst maintaining a mapping between said local network address and said Globally Routable User agent URI.