Stewart, you are like a dog with a bone. Let it go already!!!
I don't know why the f--- you keep talking about iNum. iNum is totally irrelevant to this, plus, nobody uses it. It's one of those bright ideas that someone had that never really panned out. The Obihai devices do not support iNum and neither does the Obihai network. So STFU about iNum already!
The reasons for not wanting to forward to a U.S. number could be many. If nothing else, it adds latency, and takes the call off-net (which means somebody, somewhere, has to pay for the call). In the specific case of Tropo, my suspicion is that they'd be a lot more concerned about someone using a free developer account to transfer calls if those calls were going out over the PSTN and costing Tropo money.
And anyway, the big idea here is to NOT involve additional third (or fourth or fifth) parties in the call. The more you do this, the greater the likelihood that call quality will go to hell in a handbasket.
The idea here is that the call would come direct from Tropo (or some other provider that does SIP forwarding) and come to your Obihai account. This means you do not have to use any of your SP slots, do not incur the extra latency of going through multiple providers, and don't have issues with firewalls that might block direct SIP calls. I don't know how much clearer I can make it. Your multiple (and increasingly redundant) suggestions don't accomplish those goals.
You want a specific example, show me how to route a call from Tropo to an Obihai device WITHOUT doing ANY of the following:
1) Touching the PSTN in any way (this is a HUGE no-no for me, both for technical/quality reasons and because philosophically I'm opposed to seeing a phone company get any money for a call leg that should be able to be completed over the 'net),
2) Using one of the two precious SP slots,
3) Using iNum (even if Tropo uses it, there's no way to directly route it to the Obihai device, so it's a non-starter).
4) Adding additional services in the chain of the call that increase the latency, increase the likelihood of packet loss, and could go down without notice (again, the "weakest link" principle).
5) Getting blocked by a user's (or in some cases perhaps even an ISP's) firewall (Obihai devices already connect to the OBiTALK network, and may even be able to receive calls that way when regular incoming SIP calls would fail).
You can't do it so please STOP. We already know you want additional SP slots and many of the rest of us want them too, but unless and until Obihai gives them to us, why can't we seek an alternative that might at least work from some of us? You don't have to like it but frankly I think all the solutions you've proposed so far suck, and I doubt you're going to come up with anything that would work well that does not require the use of at least one SP slot or adding an extra carrier into the call. Why do you persist in dragging this out when your posts aren't accomplishing a thing, except perhaps making me angry enough that my next post just might contain some serious profanity directed toward you, if you don't lay off (or at least come up with something original that actually meets the conditions I listed above).