NEC XN120 Feature Manual page 220

Features
n Operation
Warning Tone for Long Conversation is automatic if programmed.
Warning Tone for Long Conversation for DISA Callers:
1. A DISA caller dials into the system and places a call.
2. Once the Warning Tone is heard,
To continue the call, the DISA caller presses the programmed Continue Code.
OR
To disconnect the call, the DISA caller presses the programmed Disconnect Code.
Features Manual
218