Telephone Expansion Board (FXO) (700-15-03) (LAST TIME BUY) Date and Time Event date: Location Optional Telephone Expansion Interface for Mercury Interface Units (MIUs) Event Types Products, Trilogy Mercury System, Interface Boards Provides a standard interface for up to 4 PSTN lines or other third-party telephony devices Up to 4 Telephone Expansion Boards per MIU Allows outside callers to access the Mercury system and reach individual subscribers or conference automatically or via an operator Enables Mercury users to make and receive outside phone calls from anywhere on the system