Phantom calls can appear on Grandstream Analog Telephone adapters showing the caller ID 100 or something similar if they are not correctly programmed. These calls are not originating through IXICA but are actually coming directly from the Internet.
Here are the steps you should follow to stop these calls from appearing:
1. Log into your ATA as you normally do to program it.
2. Click on the tab called Advanced Settings
3. Find "Disable Direct IP Call" and set this value to 'yes' and apply the settings.
4. Click the FXS port tab
5. Set "Validate Incoming SIP Message" to 'yes'
6. Set "Check SIP User ID for Incoming INVITE" to 'yes' (this is optional and if you encounter incoming call problems after setting this to yes then please set it to no)
7. Set "Allow Incoming SIP Messages from SIP Proxy Only" to 'yes'
8. Apply these changes.
You should not receive these ghost calls anymore