TLS Connectivity and SIP Options
Before we start with the configuration example for Google Voice SIP Link and anynode's scenario details, please note that up to successful configurations, anynode establishes a TLS connection to Google Voice when sending SIP Options. Google Voice uses this connection to send SIP Option packets to anynode. Google Voice never establishes a TCP/TLS connection to anynode actively. All messages go through the connection that was established when the first option packet was sent. So technically, the TCP firewall may not need to be opened for incoming traffic.
Setting up Google SIP Link requires a series of configuration steps. For troubleshooting, please refer to Google's Troubleshoot SIP Link setup article article.