If you read the commission's charter broadly enough, and without regard to either the original understanding or the original intent, you come to all kinds of absurd conclusions. From the text you provided, one could, for instance conclude that the FCC has the authority to issue regulations which require parents to provide all children above the age of two with a cellphone capable of high-speed internet access with no data cap (just as easily as you could find that the FCC can regulate prison phone prices).
The FCC does not have authority to regulate phones or networks in any business or home, and cannot dictate whether your company can block certain websites or phone numbers, and the company can have a carrier set up these restrictions for them. Likewise, the FCC does have authority to regulate how phone services are provided to the prisons (though it is not clear that the FCC could discrimate prisons from other businesses), but not what happens within the prison itself or under the prison's request.
The FCC does not have authority to regulate phones or networks in any business or home, and cannot dictate whether your company can block certain websites or phone numbers, and the company can have a carrier set up these restrictions for them. Likewise, the FCC does have authority to regulate how phone services are provided to the prisons (though it is not clear that the FCC could discrimate prisons from other businesses), but not what happens within the prison itself or under the prison's request.