1. Check that your telephone and network devices (i.e. ONT or ONR) are plugged into a working power socket.​

2. Ensure that your handset is properly placed on the cradle and you have terminated the last call with the end call button  on your telephone.

3. Switch off and on the devices and wait up to 3 mins for them to restore.

You will see a green light on the Tel 1 or Tel 2 port of your ONT or ONR, and the caller will be able to reach you through your telephone successfully.