A method and arrangement in a multimedia gateway connected to a multimedia service network, for providing access to multimedia services for communication devices connected to a private network. In the multimedia gateway, a communication unit receives a request from a device in the private network for a public identity associated with the multimedia gateway. An identity manager then selects and allocates an associated public identity from a pool of public identities associated with the multimedia gateway which have been predefined as valid in the multimedia service network. The communication unit then registers the device by activating the allocated associated public identity in the multimedia service network. Thereby, the multimedia gateway can establish a multimedia session on behalf of the device, using the allocated associated public identity.