I've just been doing some thinking about these technologies, and I wondered if this is possible?
My understanding is that when a call is sent from expressway (Via B2B) using email@example.com notation, it does a lookup for the SIP SRV Record for that domain. Once it finds it, the SIP invite is then sent to that destination and the connection is established.
In the case of SIP PSTN circuits connected to a Cisco ISR CUBE gateway for regular PSTN Calling, I don't see any reason (technology capability wise) why a connection couldn't be established between that and an expressway cluster. So long as the SIP SRV is in place for the domain, we shouldn't have an issue getting the invite to the terminating ISR CUBE router.
However I cannot find any information on it. I'm sure it doesn't work, mainly because service providers wouldn't want to allow this sort of thing as it would detract from their call charge revenue - but I cant see any technological reason for it.
Any comments? Is this a thing or am I going crazy?