The 400 prefix and the new regulation for commercial calls

From October 17, 2026, calls made for commercial purposes—whether to sell or acquire customers—must be made from a number using the 400 prefix. This measure is part of the Anti-Fraud plan, which has a very specific goal: to allow users to instantly identify that it is a commercial call at a glance.

That said, it does not apply to all companies. The obligation depends on what is established in the law, which we will explain in this article.

What is the 400 prefix and what does Law 10/2025 say?

The 400 prefix is the new numbering range created exclusively for one purpose: to be the originating number for commercial calls. It is regulated by Law 10/2025 on Customer Service and is promoted by the Ministry for Digital Transformation together with the CNMC as the supervisory body for telecommunications.

The resolution explicitly states that it reinforces the need to clearly differentiate commercial calls from other types of communications, such as customer service calls or after-sales support, with the aim of improving transparency and call identification. For this reason, the 400 code is assigned.

But who does it actually apply to?

It is important to know that, although this regulation has been established for commercial calls, not all companies are required to use it.

According to Law 10/2025 on Customer Service, there are two groups required to use the 400 prefix:

1. Basic service companies, regardless of their size:
• Water, gas, and electricity supply and distribution
• Passenger transport (air, rail, sea, bus)
• Postal services
• Electronic communications
• Financial services
2. Large companies in any sector that, individually or as a group, meet the following thresholds:
• 250 or more employees
• More than €50 million in annual turnover
• More than €43 million in annual balance sheet total

Which companies are not required to use it?

If you are an SME outside these groups and you fall below the indicated thresholds, you are not required to use this prefix; you can continue using your usual numbering as before.

Energy, gas, and telecommunications companies with less than 5% national market share are also exempt on a temporary basis, as long as they do not grow beyond that threshold.

And if my company is required, when should I use the 400 prefix?

To determine whether your company needs a 400 number, the first step is to assess the actual purpose of your outbound calls.

If the call is managing an already contracted service, providing information about it, or resolving an issue, it is NOT considered a commercial call. In that case, customer service numbering is used: 800/900 numbers, geographic numbers (91, 95, 96…), or short operator numbers. Mobile numbers (6XX/7XX) and 901/902 numbers are not allowed for customer service.

If during the call an offer is made, it becomes a commercial call and must be made using the 400 prefix.

The 400 numbering as an opportunity

Although at first glance it may seem like a limitation, since we tend to assume that users will reject the call as soon as they see the number, the 400 prefix also opens the door to a positive use case in the telephony channel.

On the one hand, companies that commit to responsible and strategic use of this type of calls can differentiate themselves from others, especially in a context where users increasingly value transparency.

On the other hand, a contact who answers a 400 call will not do so by surprise, but with the intention of learning more. This can result in higher-quality conversations, as the customer is genuinely interested.

We also recommend offering an alternative contact number, such as a geographic number, for inbound calls aimed at users who are truly interested in a service and want to reach out directly.

What are the steps to obtain the 400 prefix?

The CNMC is the body responsible for assigning the 400 numbering range to telecommunications operators, who then provide these numbers to their customers.

The steps to request your 400 number are as follows:

1. First, check whether your company falls within the categories required to use this numbering under Law 10/2025 on Customer Service.
2. If so, ask your operator whether they already have 400 prefixes assigned.
3. Choose the prefix and replace the number used for campaigns with the assigned 400 number.
4. Differentiate between the sales team and the customer service team. Continue providing customer service through short numbers, 800/900 numbers, or geographic numbers, while using the 400 prefix for your sales team.
5. Take advantage of the change to review the configuration of workflows that depend on callback systems.

How to get the 400 prefix with Megacall

At Megacall, you can already purchase numbers with the 400 prefix and start using them directly for your commercial calls in the following way:

1. If you are not yet a customer, register at Megacall and access your personal area. If you are already part of Megacall, simply log in to your account.
2. Choose your 400 number from the list in order to continue making commercial calls.
3. Provide all the required documentation to obtain the number.
4. The number is activated once all the data has been verified.
5. Don’t forget to assign the number to your sales team extensions.

If you have everything centralized in a single platform such as the free Megacall PBX, you can manage all your calls—both 400 prefix and geographic numbers—in an organized and, above all, more productive way, as you gain greater control over your operations. Additionally, other advantages include:

• Calls from the same PBX, CRM, Megacall app, or web browser.
• Smart call distribution based on schedules, teams, or availability.
• Call recording and monitoring for quality control and training.
• Scalability without the need for physical infrastructure.

Summary

• The 400 prefix is used exclusively for commercial calls.
• It will be mandatory starting October 17, 2026. Operators may block commercial calls that are not made using a 400 number.
• It applies to basic service companies (water, gas, electricity, passenger transport, postal services, electronic communications, and financial services) as well as large companies.
• SMEs outside these groups, as well as electricity, gas, and telecom companies with less than 5% market share, are exempt from the requirement.
• It is only for outbound calls; customers cannot call back, and it is not intended for customer service.
• Handling an existing service, providing information, or resolving incidents is done via 900 numbers, geographic numbers, or short codes.

Reference links

Resolution of April 14, 2026 (BOE-A-2026-8409) establishing the allocation of the 400 range for commercial calls.

Law 10/2025, of December 26, regulating customer service services.

FAQs — 400 Prefix

Can users call a 400 number?

No. According to Law 10/2025, which regulates the framework, numbers in the 400 range are exclusively intended for outbound commercial calls, with no possibility of receiving inbound calls; they are one-way numbers.

What does the 400 prefix mean for companies?

On the one hand, the requirement for user consent to make commercial calls still applies. On the other hand, if the company falls within the regulated groups, commercial calls must be made exclusively using a 400 prefix number.

Can I use the same number for sales and customer support?

No. 400 numbers are only intended for sales. For customer service, support, or assistance, a geographic number or 800/900 lines must be used, as they are specifically designed for that purpose. They are complementary and one does not replace the other.

When does the use of 400 numbers become mandatory?

The regulation came into force on April 17, 2026, and includes a six-month transition period. Therefore, companies that fall within the scope of the regulation will be required to use the new prefix starting October 17, 2026.

Who assigns 400 prefix numbers to companies?

The CNMC assigns the 400 numbering range to telecommunications operators, and operators must request blocks of numbers, which are issued in batches of 1,000. Once the operator has access to the numbering, companies can request it through their operator, but never directly from the regulatory body.

Does the 400 prefix replace the Robinson List or consent requirements?

No. The 400 prefix only identifies a call as commercial. Consent obligations and advertising regulations remain in force regardless of the 400 prefix.