Let me make sure my understanding of Voice Gateways is correct: Voice Gateways were originally intended as a means for implementing 1-stage dialing through the OBiTalk interface, but as some point this was extended to allow them to work with a SIP connection as well. But, these trunks are essentially originate-only: They can be used for placing calls, but will not stay connected to a VoIP provider once that call is complete, and thus they cannot be used to receive incoming calls. They are useful for OBiTalk trunking applications, for calling out without tying up an incoming trunk, and for other specialized applications, such as wanting to present a special caller-id to the called party.
Is that about right? If not, what have I gotten wrong?