Optipoint 500 Advance is digital phone for Siemens PABX system: Hipath 4000, Hipath 3800, Hipath 3750, Hipath 3700, Hipath 3550, Hipath 3500, Hipath 3350, Hipath 3300, Hipath 1100, Hicom 300 and Hicom 150.