The following explanation is taken verbatim from the FCC regarding the USF:
Because telephones provide a vital link to emergency services, to government services and to surrounding communities, it has been our nation's policy to promote telephone service to all households since this service began in the 1930s. The USF helps to make phone service affordable and available to all Americans, including consumers with low incomes, those living in areas where the costs of providing telephone service is high, schools and libraries and rural health care providers. Congress has mandated that all telephone companies providing interstate service must contribute to the USF. Although not required to do so by the government, many carriers choose to pass their contribution costs on to their customers in the form of a line item, often called the "Federal Universal Service Fee" or "Universal Connectivity Fee."
The Federal Universal Service Fund surcharge is assessed on all interstate and international voice charges incurred by customers during the billing period. The exact surcharge rate is updated on a quarterly basis by FCC.
This surcharge is imposed for the purpose of providing telecommunications services at an affordable price to schools, libraries, rural health care providers, and low-income customers. The tax is a percentage of the interstate portion of the long distance charge on your bill. The surcharge is assessed to all telecommunications companies with interstate operations, including long distance carriers, wireless companies, pager companies and payphone companies. The Federal Communications Commission (FCC) regulates this surcharge.
This surcharge appears by many names. The following are some ways in which the FUSF charges may be represented on bills from other companies, including your local and long distance telephone carriers: