Keeping your number: porting, caller ID and spoofing when you call over the internet

Phones and numbers · Published 2026-10-24

For most people, the phone number matters more than the network behind it. It is on business cards, bank records and in hundreds of contact lists. The good news: the law in most countries says it belongs to you, not to your provider.

Number portability in the EU

Under the European Electronic Communications Code (Article 106), subscribers have the right to keep their number when switching provider within the same country, for both mobile and fixed numbers. The rules set clear expectations:

The port and activation must happen within one working day of the agreed date.
Loss of service during the process must not exceed one working day.
The new provider leads the process; you do not need to negotiate with the old one.
Prepaid customers can ask for any remaining credit to be refunded when they leave, under conditions set nationally.
Operators must compensate subscribers for delays and abuses, as set out in national rules.

National regulators implement the details. In Belgium, for example, the regulator BIPT supervises number portability; in France, the "RIO" code identifies your line for porting. Portability applies within a country; you cannot move a Belgian mobile number to a French operator.

Number portability in the United States

The FCC's local number portability rules let customers keep their number when switching between wireline, wireless and interconnected VoIP providers in the same area. The FCC requires "simple" ports to be completed within one business day. A provider may not refuse to port your number because you still owe an early-termination fee, although you remain liable for any fees in your contract.

Can a VoIP app use your existing number?

There are several distinct situations, often confused:

Carrier Wi-Fi calling and VoLTE use your number natively; nothing to set up.
Porting the number to a VoIP provider. In many countries you can move a fixed, and sometimes a mobile, number to a VoIP provider, which then rings it on apps and desk phones. Your mobile SIM stops working on that number once the port completes, so this suits office lines more than personal mobiles.
Caller ID presentation. Some VoIP-to-phone services let you verify that you own a number (usually with a code sent by SMS or call) and then display it as your caller ID on outgoing calls, while incoming calls still arrive on your SIM. Calling services of the early 2010s relied on this approach to let customers "call with their own number". Whether this is allowed, and how the number must be verified, depends on national rules.
App identities. WhatsApp, Signal and similar apps use your number only as a sign-up identifier. They do not route calls to or from the telephone network.

Caller ID spoofing

Caller ID was designed in an era when only a few trusted operators could inject numbers into the network. VoIP made it easy to send any number, which fraudsters exploit to impersonate banks, government agencies or local numbers. Responses include:

United States: the Truth in Caller ID Act prohibits spoofing with intent to defraud or cause harm. Under the TRACED Act, the FCC required voice providers to implement the STIR/SHAKEN caller authentication framework in their IP networks, with a main deadline of 30 June 2021 (FCC call authentication page). Calls are digitally signed by the originating provider so the receiving network can check whether the caller is entitled to use the displayed number.
United Kingdom: Ofcom has required providers to block calls from abroad that falsely display UK landline numbers, and publishes consumer guidance on scam calls.
EU countries: several regulators have introduced national measures against spoofed numbers, for example blocking incoming international calls that display a domestic mobile number. Approaches differ from country to country.

For you, the lesson is simple: a familiar number on the screen proves nothing. If a caller asks for codes, passwords or payments, hang up and call back on a number you find yourself.

Protecting your number from hijacking

Porting and SIM replacement processes can be abused to take over someone's number and intercept SMS verification codes. To reduce the risk:

Set a PIN, passphrase or port-out lock on your operator account if available.
Use an authenticator app or security key, rather than SMS, for important accounts.
Act immediately if your phone suddenly loses service for no reason: contact your operator from another phone.

Before switching provider

Do not cancel the old contract yourself first; let the new provider request the port, or the number may be lost.
Have your account number or porting code ready.
Expect a short interruption on the switch day, and keep a way to receive important SMS codes.