Segments from the troubleshooting EC500:
https://downloads.avaya.com/css/P8/documents/100010637
The user reports that the cell phone is receiving a switch default caller identification number for calls from the Avaya server running Communication Manager.
The ISDN Service Provider (SP) is replacing the caller identification with a fixed caller ID.
Escalate the issue to your Telecom Manager who may contact your ISDN SP to request that this be fixed or find an alternate ISDN SP that allows the caller identification to pass.
The switch is blocking the outgoing caller identification and is passing a default caller ID.
Change your switch administration to allow caller identification to go outside the switch
Arbi