Why are Toll-free number prefixes different?

In terms of functions or performance, there is no difference among all Toll-free number prefixes. 
Calls made to Toll-free numbers with different prefixes will be free of charge and have equal quality. 
Toll-free numbers are commonly called "800 numbers" after the original area code.  With the expansion of Toll-free numbers, new area codes with different prefixes are being added to numbering plans.