Yeasta Module O2 Used to customize a phone system connection compatible with the Yeastar MyPBX or S-Series This module allows FXO connection on two ports to connect two PSTN analog lines (POTS) Also fits into one of the built-in module slots in the S412, S20 and S50 Requires Expansion board to fit S100 or S300 units. Features of the Yeastar O2 Module Provides 2-port FXO connectivity on the Yeastar IP-PBX module. Allows connection of a VoIP system to POTS (analog) telephone lines. The Yeastar O2 module is compatible with Yeastar S series (S20, S50, S100, S300, S412). Yeastar MyPBX SOHO. Yeastar MyPBX Standard. Yeastar MyPBX U100. Yeastar MyPBX U200 .Yeastar MyPBX U500 series.