Complex sentence: Where telephone access is widely available, dial-up remains useful and it is often the only choice available for rural or remote areas, where broadband installations are not prevalent due to low population density, and high infrastructure cost.
Split into simpler sentences: Where telephone access is widely available, dial-up remains useful. Broadband Dial-up is often the only choice available for rural or remote areas, where broadband installations are not prevalent due to low population density, and high infrastructure cost.