Complex sentence: Many millions of Model 500 phones were produced and were once a familiar sight in almost every home in America; huge numbers are still in use today thanks to their unparalleled durability and to their cheap prices and ample availability on the secondhand market.
Split into simpler sentences: Many millions of Model 500 phones were produced and were a familiar sight in almost every home in America. Numbers of WE 500 phones are still in use today thanks to their unparalleled durability, their cheap prices, and ample availability on the secondhand market.