2.11.  Sending DTMF signals  
During a conversation you sometimes have to send DTMF signals, such as with a voice server, an 
automated attendant or a remotely consulted answering machine. 
  During a conversation 
  Send DTMF 
  Enter DTMF code 
The function is automatically cancelled when you hang up. 
2.12.  Mute, so that your correspondent cannot hear you  
You can hear your correspondent but he/she cannot hear you:  
From the set 
  During a conversation 
   Disable microphone   The key lights up   
   Resume the conversation   The key is no longer lit   
From the Bluetooth® receiver  
   Press the handset volume/mute key (long press)