You can use the DND feature to reject the incoming calls automatically on the phone and the callers can hear a busy signal or a message depending on your server.

To activate DND in phone mode:

1. Press the DND soft key when the phone is idleThe  icon on the idle screen indicates that the Do Not Disturb mode is enabled. Incoming calls will be rejected automatically and "n New Missed Call(s)("nindicates the number of the missed callswill prompt on the LCD screen

To activate DND in custom mode for a specific account:

1. Press the DND soft key when the phone is idle. 
The LCD screen displays a list of the accounts on the phone.

2. Press Up or Down to select the desired account.
3. Press Left or Right soft key to select On to activate DND.
4. Press the Save soft key to accept the change. 
The  icon appearon the idle screen and the specific line icon changes to ico.