The USF fee (Universal Service Fund) is required by federal law to be charged by all long distance service providers. The Federal Communications Commission (FCC) sets the USF rate each quarter. The current rate can be found listed at the FCC website from here.
If the current USF fee is 9.5%, that means if you were to make $10.00 in long distance calls during the month, you would be charged a USF fee of $0.95 for that bill.
The fund offers support to telecommunication carriers in rural and high-cost areas, low-income consumers, schools, libraries and rural health care providers.