With some traditional VoIP calls, the ISP is merely a transport to another provider. If your internet service provider offers VoIP technology through their own lines (BellSouth/AT&T, Comcast, etc), then that would be the only time the internet service provider would also be your carrier. Otherwise, someone else always is the carrier to your ISP's transport.
For example, Comcast cable modem with Vonage phone service. With T-Mobile's UMA service, your ISP will be the transport, but T-Mobile will still be the carrier (your usage takes away from your monthly minutes).
In the beginning the Universe was created. This has made a lot of people very angry and is widely regarded as a bad move.