The days of deceptive commercial calls are numbered: When does the 400 prefix start?

From next October, all commercial calls must be made from a nine-digit number starting with the code 400, which will allow users to easily identify these calls.

The measure was approved by the Ministry for Digital Transformation and Public Function and in two months operators will have to block calls that are not made from the assigned numbering.

This complies with the Customer Service Law (SAC), approved last December, which included the need for commercial calls to have a specific numerical code.

Numbers starting with the code 400 will be unidirectional, meaning users will only be able to receive calls. This further guarantees customer protection, as it avoids possible fraudulent practices that could occur when returning a call to an unknown number.

The measure comes into effect on October 17, 2026. From that day, the six-month adaptation period will be met for operators to adapt their networks and automatically block any telemarketing call that is not made from a 400 number.

"We have all suffered calls from a mobile phone at some point that we answered thinking it was a family member or a friend and then it turned out to be a commercial call. From October, we will all be able to identify if it is commercial," explained the Minister for Digital Transformation and Public Function, Óscar López.

In addition, he has thanked "the collaboration, effort, and work of the telephone companies that are supporting the Government and the Ministry" both in this measure and in the implementation of the Anti-phone scam plan. A plan with which, López recalled, "we have managed to block 192 million calls and 17 million SMS messages" since its approval in March of last year.

The published resolution also recalls that telecommunications operators can offer their customers the option to disconnect from the commercial call service provided through the 400 range.

If you receive commercial calls from numbering not assigned for this service, users can report it to the Telecommunications User Service Office (OAUT) or the CNMC.

Likewise, in another resolution, the Ministry for Digital Transformation and Public Service establishes that customer service calls shall only be made from the short numbers specifically assigned for this purpose, the 800 and 900 toll-free ranges, or geographic numbers.