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 telephone numbering range created for a single purpose: to serve as 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 of April 14, 2026 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 services, 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.

If I am a regulated company, when should I use the 400 prefix?

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

When the objective is to offer a service—whether it is a new subscription, an upgrade, or a renewal—it is considered a commercial call and must be made from a number with the 400 prefix. On the other hand, if the communication is related to a service the customer already has active, such as providing updates, giving support, or solving an issue, it is considered customer service and can still be carried out using geographic numbers or 800/900 numbers.

If during a customer service call an offer is introduced—for example, an agent calls to confirm that the PBX is working and takes the opportunity to offer the CRM—the call would then be transferred to the sales team using 400 numbering, since it is considered a commercial call.

Regarding the use of mobile numbers, it is prohibited under Order TDF/149/2025 both for commercial calls without consent and for customer service, as well as 901 and 902 lines.

How to get the 400 prefix with Megacall

At Megacall, you can already purchase 400 prefix numbers and start using them directly in your commercial calls as follows:

1. Access your account. If you are not yet a customer, you can create your account and access your personal area in just a few minutes.
2. From the “Connect number” section under Services, select Spain and, in the list of cities, choose “Commercial calls.” Choose your 400 number from the list. As with geographic numbers, you will have the option to select a standard, gold, or silver number.
3. Provide the required documentation to obtain the number. For 400 numbering, you will need to submit: a copy of the company registration certificate and the current address, including street, number, postal code, and city.
4. The number will be activated once all the data has been verified and will then be ready for use.
5. Assign the 400 number to your sales team’s extensions so that it appears in outbound calls.

As it is integrated into the same PBX, you can manage the 400 number alongside the rest of your numbers (geographic, 900, etc.) without changing providers or tools. In addition, there are other advantages:

• Make calls from the same PBX, CRM, the Megacall app, or directly from a web browser.
• Unified management of inbound and outbound calls from a single platform.
• Intelligent call distribution based on schedules, teams, or availability.
• Recording and monitoring for quality control and training.
• Scalability without the need for physical infrastructure.

Final checklist for your PBX with the 400 prefix before October 17

You can use the following list to make sure everything is ready by October 17.

PBX configuration

• Assign the 400 number to the sales team extensions.
• Set the 400 number as the outbound caller ID for campaigns.
• Review outbound rules to prevent commercial calls from being made with other numbers.

Call flow

• Keep customer service on 800/900 numbers, geographic numbers, or short numbers.
• Review voicemail boxes and automated messages.
• Always include an alternative number for callbacks.
• Review call schedules and adjust them to time slots with better response rates.

Final tests

• Make test calls from the 400 number
• Check how the number appears on the device
• Adjust campaigns based on the initial results

FAQs — 400 Prefix

Can users or customers call a 400 number?

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

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

No. 400 numbers are only intended for sales. To provide customer service, assistance, or support, you need to use a geographic number or 800/900 lines, which are specifically designed for that purpose. They are complementary and do not replace each other.

From when will the 400 numbering be 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 the numbers, which are provided in blocks of 1,000. Once the operator has the numbering available, 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 identifies a call as commercial, but it does not change existing legal obligations. To make calls, you still need user consent or a legitimate interest. In addition, the Robinson List still applies—if a user is registered and you do not have authorization, you should not call them, even if you are using a 400 number.

How many simultaneous calls does the 400 prefix allow?

Numbers with the 400 prefix allow up to 5 simultaneous calls within the Megacall PBX. This means that multiple agents can use the same number at the same time without interruptions.

Can the 400 number be used from a CRM or app?

Yes. It can be integrated into a CRM and applications, as well as the virtual PBX, allowing commercial calls to be made directly from these tools, wherever you are.

What happens if I continue making commercial calls using a number that is not 400?

From October 17 onward, operators may block numbers identified as commercial calls that are not made from a 400 prefix. This may be subject to penalties as a consumer law infringement.