For a century, every telephone had a pair of copper wires coming out the back that ran through the house, up onto the poles, and along the street to the telephone company building. There the number for that telephone was tied in to the particular wire pair and thus, by way of the wire, to the house where the phone sat. A telephone number specified not just a telephone, but a location.

The advent of cell phones broke the link between number and location. Suddenly a person could call a number and have no idea where on the continent it might ring. Still, some numbers were assigned to cell phones and others to wired phones. The numbers looked the same (at least in the U.S.), but a given number was either one or the other.

Interconnected VoIP phones — those that send calls over the Internet to and from ordinary telephones — made those numbers truly global. Now a call to a local number might reach any point on the planet.

Adding to the potential confusion, the FCC four years ago allowed consumers to carry the same phone number from wireline to wireless service, so that a previously fixed number could overnight become mobile.

Last week the FCC brought the process of uncertainty to its logical conclusion, announcing that wireline and wireless phone numbers can be transferred to and from interconnected VoIP service. Think about this. A person can move from New York City to Dubai, say, and keep his old phone number with the old 212 area code. And still be a free local call to his friends back in New York.

VoIP started out like most other Internet offerings, as an “information service” free of regulation. Because it is largely interchangeable with conventional voice service, however, the FCC has been regulating it as such, one step at a time. The new portability requirements add to earlier rules on TRS (for access by disabled users), CALEA (for law enforcement wiretaps), E-911 (to locate emergency callers), Customer Proprietary Network Information (for privacy), and the Universal Service Fund.