Modules and Boards

Yeastar SO PSTN Fallback Module

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Yeastar SO PSTN Fallback Module (YST-SO)

The Yeastar SO Module is used to customize the connectivity of a compatible Yeastar MyPBX or S-Series phone system. Specifically, this module enables one FXS port and one FXO port for the addition of an analog telephone and one analog PSTN (POTS) line. Additionally, this module has a unique PSTN Fallback function, enabling you to make/receive calls even when the system powers down.

This module fits into one of the on-board module slots for the S412, S20, and S50. It requires an expansion board to fit into the S100 or S300 units.


  • Enables one FXS and one FXO port
  • Allows for addition of 1 analog telephone and 1 analog line
  • Unique PSTN Fallback function for making and receiving calls when power fails


  • Yeastar S-Series (S20, S50, S100, S300, S412)
  • Yeastar MyPBX SOHO
  • Yeastar MyPBX Standard
  • Yeastar MyPBX U100
  • Yeastar MyPBX U200
  • Yeastar MyPBX U500 Series

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