Voice-IP system is properly considered an information service, as the data is transformed to the traditional telephony format before entering the network. State regulation therefore preempted by the field of federal law.
Dissent: There is no noticeable transformation between end users, some networks use voice-IP internally, transforming to traditional format before routing to user.
http://media.ca8.uscourts.gov/opndir/18/09/172290P.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.