But that the LINE port is for plugging into a live phone line. I don't know why you would want to do that but...
With the OBi LINE Port connected to your incoming Verizon phone line, all telephones can be connected to the OBi PHONE Port. The OBi PHONE Port can then access both VoIP services as well a landline services from the same set of telephones.
The OBi is also capable of forwarding calls between services. For example, you might have the OBi forward incoming calls on your Verizon line to your cell phone using Google Voice.