Network device for managing a call between user terminals, configured to check whether a first user terminal supports a usage of a first audio coding mode for the call, and a second user terminal intends to use a second audio coding mode for the call; if the first user terminal supports the usage of the first audio coding mode for the call, and the second user terminal intends to use the second audio coding mode for the call, repack first data of the call sent from the first user terminal to the second user terminal and packetized into first packets referring to the first audio coding mode, into second packets referring to the second audio coding mode; and repack second data of the call sent from the second user terminal to the first user terminal and packetized into third packets referring to the second audio coding mode, into fourth packets referring to the first audio coding mode; wherein the network device is further configured to check whether a first initial call offer sent from an originating user terminal to a terminating user terminal indicates a usage of the second audio coding mode for the call; if the first initial call offer indicates the usage of the second audio coding mode for the call, intercept the first initial call offer and forward a second initial call offer to the terminating user terminal instead of the first initial call offer, the second initial call offer indicating a usage of the first audio coding mode for the call; check whether a first answer to the second initial call offer, sent from the terminating user terminal to the originating user terminal indicates the usage of the first audio coding mode for the call; if the first answer indicates the usage of the first audio coding mode for the call, intercept the first answer and forward a second answer to the originating user terminal instead of the first answer, the second answer indicating the usage of the second audio coding mode for the call; and assert that the terminating user terminal supports the usage of the first audio coding mode for the call and the originating user terminal intends to use the second audio coding mode for the call so that the terminating user terminal is the first user terminal and the originating user terminal is the second user terminal. repack first data of the call sent from the first user terminal to the second user terminal and packetized into first packets referring to the first audio coding mode, into second packets referring to the second audio coding mode; and repack second data of the call sent from the second user terminal to the first user terminal and packetized into third packets referring to the second audio coding mode, into fourth packets referring to the first audio coding mode; intercept the first answer and forward a second answer to the originating user terminal instead of the first answer, the second answer indicating the usage of the second audio coding mode for the call; and assert that the terminating user terminal supports the usage of the first audio coding mode for the call and the originating user terminal intends to use the second audio coding mode for the call so that the terminating user terminal is the first user terminal and the originating user terminal is the second user terminal.