To activate ISDN-type services and features through the network carrier's analog trunks or those of other communications platforms (such as "consultation hold"), you must send a signal to the trunks before dialing the service code or telephone number. 

Precondition: You have set up an external connection. 

Press the key. The LED lights up. 

Select and confirm. 

Enter the code. 

Enter the service code and/or telephone number.