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Glossary · Numbering

What is Number porting?

  • Also called: lnp, local number portability, port a number

Reviewed by Sujan ThapaliyaLast updated

Definition

Number porting moves a phone number from one provider to another while keeping the number itself. The number stays reachable throughout, which is why porting rather than replacing is how a business changes provider without telling its customers to update anything.
The three STIR/SHAKEN attestation levels, which underpin how number porting behaves in practice: A asserts both that the carrier knows the customer and that the customer may use the calling number, B asserts the customer only, and C asserts neither. A shared number pool can reach B at best, which is why number ownership keeps recurring in these definitions.
Attestation is the backdrop to most caller-ID and deliverability terms, number porting included.

In practice

How number porting actually works

The process is administrative rather than technical: the gaining provider requests the number, the losing provider validates the details against its records, and a date is agreed. Most rejections come from a mismatch in the account details on the request.

Numbers cannot be ported while an account is in dispute or the number is suspended, which is why porting should be started before cancelling anything.

A provider that makes porting out difficult is telling you something about what leaving will look like, and it is a fair question to ask during evaluation rather than after.

Porting also has a quiet failure mode worth planning around: services attached to the number that do not move with it. Voicemail boxes, SMS registration, emergency address records and any integration keyed to the old carrier all need re-establishing, and discovering that after the cutover is how a clean port turns into an outage.

Worked example

Most rejections come from one mismatch: the account number, billing address or authorised contact on the request not matching the losing provider's record. Copy them from a recent bill rather than from memory.

Number porting: common questions

How long does porting take?
Days rather than hours for most numbers, and longer for toll-free and for complex business accounts. The variable is validation against the losing provider's records, not the technical switch.
Will my number stop working during a port?
No. The number keeps ringing on the old provider until the cutover, which is typically a short window on the agreed date.
Why do ports get rejected?
Almost always a mismatch between the details on the request and the losing provider's records — account number, billing address, or the authorised contact name. Copy them exactly from a recent bill.

Sources

  1. Combating Spoofed Robocalls with Caller ID Authentication — Federal Communications CommissionThe STIR/SHAKEN framework, the attestation levels carriers sign calls with, and the mandate requiring providers to authenticate caller ID.
  2. 47 U.S.C. § 227 — Restrictions on the use of telephone equipment — Cornell Legal Information InstituteThe Telephone Consumer Protection Act itself — the consent requirements, calling-hours limits, and private right of action.
  3. ITU-T Recommendation E.164 — The international public telecommunication numbering plan — International Telecommunication UnionThe international number format, the 15-digit maximum, and how country codes and national numbers compose.

See number porting in the product

A toll-free number is one the called business pays for rather than the caller. In North America they use the prefixes 800, 833, 844, 855, 866, 877 and 888, which are functionally identical — the newer ones exist only because the older ones ran out. They signal national reach; a local number signals proximity.

Explore toll-free numbersGet early access