[Asterisk] How to turn your OBi20x device into a SIP-to-GVSIP bridge

I wanted to get this out before June 18th and have finally gotten the document into reasonable shape: https://cboh.org/voip/obi/OBi_As_ITSP.html The document describes how to configure a FreePBX Asterisk server and an OBi20x device to allow the latter to serve as a SIP-to-GVSIP bridge for the Asterisk server. It provides another option for continued Asterisk support for GV in the (presumed) post-XMPP era. It is published in the hope that these instructions prove useful to those running Asterisk and employing GV lines as trunks.