Sometimes, the user will receive strange calls which are not from registered SIP server;
these are so called ghost calls. It will disturb and confuse the user.
IP Call feature allow the SIP phone to make and receive calls by IP address (Without SIP account)
Enable or Disable IP Direct Call feature:
WEB UI path:
Features->General Information-> Allow IP Call
（T32G/T38G can't support configure it through the web UI）
Auto provisioning parameter:
# 0-disable; 1-enable; default value is 1 (Enable)
2. Enable SIP trust feature:
SIP Trust feature allow the phone to only accept the message from the trusted server for specific account.
Only by auto provisioning parameter:
# 0-disable; 1-enable; default value is 0 (Disable)
Only the version is V80 or higher support configure it through the web UI.