So.. I read in some article that provisioning phones behind a functional SBC should work. I have not yet gotten any 3CX Phone to provision behind an SBC. Seems that the multicast is getting forwarded as prescribed.. but I cannot add/create an extension and have the phone actually provision. 3CX Phone or.. Yealink SIP-T21. Given the VPS options are looking more and more appealing.. as is a multi-tenant approach.. would be nice to have this actually work. I can do small setups a bit more semi-manually.. but provisioning handsets at the console sure is ideal (when on the LAN.. would like the SBC part to also work). These have been the rPi SBCs of vanilla builds. Manual config for the Yealink or 3CX Phone (or a Cisco.. but http resync is fine) will use the SBC.. so I know the connectivity/auth for the SBC is solid.