With the paid ES-Voicebox License 6, you can expand your system (ES 54x, ES 6xx, and ES 7xx) by an additional 6 voiceboxes each. You can book the license up to 2 times on the ES 54x series communication systems, up to 3 times on the ES PURE-IP 20 IT, up to 4 times on the ES 6xx, up to 9 times on the ES 730 IT, and up to 18 times on the ES 770 IT. This allows you to increase the number of voiceboxes on an ES 542 to a maximum of 12, on an ES 546, ES 548, and ES 548 IT to a maximum of 18. The ES PURE-IP 20 IT can accommodate up to 24 voiceboxes, the ES 6xx communication systems can support up to 30 voiceboxes, the ES 730 IT can handle up to 60, and the ES 770 IT can support up to 120 voiceboxes.