Your fax number is on every business card, every prescription pad, every vendor contract, and probably a sticker on the front desk. Switching providers without changing that number is what keeps the move from being a disaster. The technical term is "porting," and it is a well-established process, but it is also the place where most provider migrations go sideways.
Here is how it actually works, what the paperwork really says, and how to keep every inbound fax during the transition.
What "porting" actually means
A phone number is not owned by the carrier you currently buy service from. It is licensed to that carrier by the regulator and assigned to your account. When you port, you are asking your new carrier to take over the licensing of that specific number. The old carrier is required by FCC rule to release it within a defined window, assuming the paperwork is correct.
For fax, this matters because the number itself is what your senders dial. The provider behind the number can change without anyone calling you ever knowing. Done correctly, a port is invisible to the outside world.
The LOA (Letter of Authorization)
The single most important document in the process is the LOA. Every carrier has their own form, but they all ask for the same things:
- The exact business name on the current account, character for character
- The service address on file with the current carrier
- The billing telephone number, which is sometimes different from the number you're porting
- The account number with the current carrier
- A signature from someone authorized on the account
- The list of numbers being ported
The LOA is what your new provider submits to the old one to prove you actually want the move. It is also the single most common point of failure. If the business name on your eFax account says "Smith Dental, PC" and your LOA says "Smith Dental Practice," the port will reject and you will get a rejection notice with no useful detail.
Pull your most recent invoice from your current provider before you fill anything out. Match the LOA to it exactly.
Typical timeline
Once a clean LOA is submitted, the standard porting window is 5 to 10 business days for U.S. and Canadian numbers. Toll-free numbers are usually on the faster end of that range. Local numbers depend on the losing carrier — some release in three days, others use the full ten.
International numbers vary widely. UK numbers typically take 10 to 15 business days. EU country numbers can stretch to 20 or more depending on the local regulator.
Plan for the long end of the window. Do not cancel your old service before the port confirms.
What to do during the porting window
The port itself happens at a specific moment — usually overnight on the scheduled date — but during the days leading up to it, both providers technically have the number. You want a fallback path in case anything routes oddly during the cutover.
The easiest fallback: ask your new provider for a temporary fax number when you sign up. Most provide one immediately. Use that number for outbound during the transition so any reply faxes route into the new system regardless of where the inbound number is currently pointing. After the port completes, you can release the temporary number or keep it as a backup.
For inbound, the old provider continues to deliver until the port date. You will not miss anything if you simply leave the old account active until 24 hours after the port confirms.
Common pitfalls
Three failures account for the vast majority of port rejections.
- Account-name mismatches. The single most common rejection. Fix by matching the LOA to your last invoice exactly, including punctuation and entity suffix.
- Billing-address differences. If you moved offices and never updated the old carrier, the address on their account does not match your current address. The port will reject. Update the address with the old carrier first, then submit the LOA.
- Pending account changes on the old carrier. If you have an open ticket — disputed bill, address change, plan change — the old carrier can suspend porting until the ticket closes. Resolve all open tickets before submitting.
Step-by-step checklist
- Pull your most recent invoice from your current fax provider
- Confirm the business name, service address, and account number on that invoice
- Resolve any open tickets or disputes with the current provider
- Sign up with your new provider and request a temporary fax number for the transition
- Submit a clean LOA matching your invoice character-for-character
- Wait for porting confirmation, typically 5 to 10 business days
- Test inbound and outbound on the new provider once the port confirms
- Keep the old account active for 24 to 48 hours after confirmation as a safety margin
- Cancel the old provider in writing once everything routes cleanly
Done in this order, the port is uneventful. Done in any other order, you will spend an afternoon on the phone with two carriers.