In WebEx Calling, Between Different Organizations

[THOMAS CARROLL]

Can Calls be made via Dialing E164 numbering between WebEx Organizations without Egress/Ingress PSTN connectivity?

[Dennis1432]

Only inside the same domain, calls will route internally, if call is from Domain A to Domain B, it has to route via DID. 

[Mohammed-A.R.A]

Correct. Inter-Org-Calls are always routed via PSTN. 
Its your carrier/PSTN provider who owns the number and they will route the call. 
It depends who is offering PSTN services. It can be through local gateway, Cisco provided PSTN service or partner provided PSTN service.

[Vaijanath Sonvane]

You can use local gateway between two Webex Calling organizations to allow Inter-Org-Calls.

[dtibbe · Accepted solution]

Nope. Inter-Org-Calls are always routed via PSTN.