There are five different call types. Local calls are the most common.
Interlata calls are within your region, but are subject to higher charges than local rates. Usually such calls will be within your own are code.
Intrastate calls are within your own state. Since intrastate calls are subject to different taxes than Interstate calls, it can sometimes be more expensive to call within your own State.
Interstate calls are outside your state.
International calls are outside the United States.
Theoretically you could have a different company handling each type of call. However, monthly fees or minimum call volume make it more common to choose one company for the other calls.