https://en.wikipedia.org/wiki/Universal_Service_Fund. The 18% rate is paid on some part of the total bill that the FCC deems to be related to interstate voice, with additional state USF fees paid on intrastate services. Historically, telcos didn't pay money into the USF for broadband (except to the extent they're offering telephone service over it), but historically they also couldn't get money out of it for broadband. Under Obama the USF started conversion into a broadband fund, and USF taxes on broadband will likely follow.