Yes Obihai registering an ITAD is what I was suggesting, but rather than requiring a separate setup, that the data Obhai already has be used. Since the OBi's already register to OBiTalk network, and have unique OBitalk numbers, they handle winding thru your firewall without having to punch a hole in your security and also accommodate dynamic ip's. So say any OBiTalk number * OBhai's ITAD would ring the OBiTalk device, without the calling device itself having to be registered to the OBiTalk network, via a redirection from the OBihai server. This would require I suspect only minor changes on Obihai servers. Dial string parsing with any number followed by * followed by any number again would be fewer key presses and make it easier for the user to dial.
To allow the OBi devices to easily use ISN to contact other non-OBiTalk ISN systems then what would be nice is for the OBi device firmware to handle native (5.1.1 from the cook book) ISN lookups itself, rather than require the setup of a proxy, to make it easier for users. This would of coarse also mean that outgoing sip dialing be handled by the OBi device without the needing to have a sip provider enabled to place the outgoing call, again for the simplicity of the user.