Complex sentence: With Bell System divestiture, the network in the US was divided into Local Access and Transport Areas (LATAs), calls within which were carried by Local Exchange Carriers (LECs), while calls between them were carried by Interexchange carriers (IXCs).
Split into simpler sentences: With Bell System divestiture, the network in the US was divided into local access and transport areas (LATAs). Calls within LATAs were carried by Local Exchange Carriers (LECs), while calls between them were carried by interexchange carriers (IXCs).