I am aware of the link you quoted, however I think it is specific for the integration of the SPA3102 and SPA9000 on the same LAN, (an alternative way to go PSTN rather then using SAP400). Correct me please if I am wrong.
I am analyzing it in case I go VPN (WRV210) (WAN setup).
This configuration, although technically feasible (need VPN between the sites and a router that perform port forward for all RTP and SIP ports) is not supported, so we dont have any documentation for it.
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