Number portability is a subscriber's ability to keep a telephone number when moving to another carrier. The US rules define it as the ability "to retain, at the same location, existing telecommunications numbers without impairment of quality, reliability, or convenience when switching from one telecommunications carrier to another" (47 CFR 52.21(m), https://www.law.cornell.edu/cfr/text/47/52.21, accessed 27 September 2026), and 47 U.S.C. 251(b)(2) (https://www.law.cornell.edu/uscode/text/47/251, accessed 27 September 2026) makes providing it, to the extent technically feasible, a duty of every local exchange carrier. The number moves. The block it was issued from does not, and the regulator's allocation table goes on listing the carrier the block was given to.
What Spaw answers
carrier, carrier_code and carrier_brand name the holder of the number's block as the regulator's table records it, or, where no table answers, carrier names the network the numbering metadata's prefix data gives for the range: the original allocation either way, never who serves the number today. line_type and is_virtual read the same holder where it settles them, so a number ported away from a VoIP provider's block still answers voip and scores the virtual signal (+40), and a number from a wireless carrier's block that was later ported to a VoIP service still answers mobile. block_assigned_at dates the block, not the day the current subscriber got the number.
Only a query into the carrier networks can say whether a number was ported and who serves it now. The answer keeps that in fields of its own, ported, current_carrier, reachable and roaming, which stay null until a live check has answered, so the table's answer and the network's are never blended. The live carrier-network check (hlr: true) is not enabled on the service: hlr_checked answers false and nothing extra is charged.
What it does not mean
A carrier read from a block is not wrong after a port; it answers a different question. It says who the numbers were issued to, which is what a regulator's table can prove, and the phone intelligence guide says so where it lists the sources. A port also leaves the number's code where it was: the number keeps its area code and the rate centre its code was assigned in, so region describes where the number was issued before and after the move, never where the subscriber is. Nothing in the answer names the subscriber either, because Spaw does no reverse lookup. The US block tables are summarised on the United States phone facts.