The geographic areas in each state in which long distance calls are carried are known as LATAs (Local Access Transport Areas). Calls that originate and terminate in the same LATA are IntraLATA calls.
Calls that originate in one LATA and terminate in another LATA in the same state are called InterLATA calls. Calls placed from Montana to another state are Interstate calls. Montana is divided into two main LATAs, which roughly divide the state in half from northwest to southwest.
The northwest corner of the state, including the Libby, Eureka and Troy area, is in a third LATA, which also includes the Idaho Panhandle.