Method for packet-oriented transmission of voice data and optionally audio, video and/or useful data between an internal data network and a public data network, with the following process steps: a) transmitting a request of an internal multimedia computer to a NAT address server (NAT: Network Address Translation) for making available an advance NAT address to an IP address (IP: Internet Protocol) of the internal multimedia computer; b) allocating an advance NAT address to the IP address of the internal multimedia computer through the NAT address server; c) sending a current allocation data set between the advance NAT address and the IP address of the internal multimedia computer of the NAT address server to a NAT hose; d) sending the advance NAT address of the internal multimedia computer from the NAT address server to the internal multimedia computer; e) sending a data packet with voice-over-IP protocol data, which contains the advance NAT address as voice-over IP address, from the internal multimedia computer to the NAT host; f) exchanging a source indication in the header of the data packet, which contains the IP address of the internal multimedia computer, via the NAT host against the associated advance NAT address, g) forwarding the data packet via the NAT host to an externally addressed computer; h) receiving a data packet with the advance NAT address from the externally addressed computer via the NAT host; i) retrieving the current allocation data set from the NAT host against the NAT address server; j) exchanging a target indication in the header of the data packet (IP header), which contains the advance NAT address, against the associated IP address of the internal multimedia computer using the current allocation data set via the NAT host; k) forwarding the data packet via the NAT host to the internally addressed multimedia computer. a) transmitting a request of an internal multimedia computer to a NAT address server (NAT: Network Address Translation) for making available an advance NAT address to an IP address (IP: Internet Protocol) of the internal multimedia computer; b) allocating an advance NAT address to the IP address of the internal multimedia computer through the NAT address server; c) sending a current allocation data set between the advance NAT address and the IP address of the internal multimedia computer of the NAT address server to a NAT hose; d) sending the advance NAT address of the internal multimedia computer from the NAT address server to the internal multimedia computer; e) sending a data packet with voice-over-IP protocol data, which contains the advance NAT address as voice-over IP address, from the internal multimedia computer to the NAT host; f) exchanging a source indication in the header of the data packet, which contains the IP address of the internal multimedia computer, via the NAT host against the associated advance NAT address, g) forwarding the data packet via the NAT host to an externally addressed computer; h) receiving a data packet with the advance NAT address from the externally addressed computer via the NAT host; i) retrieving the current allocation data set from the NAT host against the NAT address server; j) exchanging a target indication in the header of the data packet (IP header), which contains the advance NAT address, against the associated IP address of the internal multimedia computer using the current allocation data set via the NAT host; k) forwarding the data packet via the NAT host to the internally addressed multimedia computer.