Billion BiPAC 7401VP User Manual page 81

Attention
Chapter 4: Configuration
The following situation will make phone port 1 and 2 relay to PSTN line
automatically.
-
Power down
-
Internet Service fail, i.e., lost of WAN IP Address
-
SIP service is not accessible. This excludes when:
User manually disables Registration.
User inserts a wrong authentication username or password.
User dials a wrong SIP number.
VoIP/(802.11g) ADSL2+ Router
80