Comdial DXP, DXP Plus, FX Attendant Manual page 148

Speakerphone Characteristics
Depending on the telephone line conditions and the type of speaker-
phone at the other end, it may not be possible for the 8324F-** to
operate in full-duplex mode. If the speakerphone at the other end is a
half-duplex speakerphone and both parties are in speakerphone mode,
the half-duplex speakerphone is the controlling factor, preventing the
8324F-** from operating in full-duplex mode.
Note: Pressing any button (mute, hold, etc.) on the speakerphone
while in full-duplex mode causes the system to perform the
"speech training" test again. For example, if you press MUTE
while in full-duplex mode, when you release the call from mute,
the system will perform the entire "speech training" test again.
138 Comdial August, 03