Prefix 400 for spam calls arrives in Spain soon

In less than two weeks, mobile phones in Spain will start displaying a new prefix, 400, when receiving certain calls. This initiative was announced six months ago and aims to provide users with an additional filter to recognize unwanted calls before answering. While the measure has been well-received in theory, distrust towards similar initiatives remains among users.

## Why it matters The introduction of prefix 400 is significant as it represents a government effort to combat the growing issue of spam calls. With the rise of unsolicited commercial calls, this measure could help users identify and avoid unwanted interactions, enhancing their telephone experience.

## What we know In April, the Spanish government published a resolution in the Official State Bulletin, establishing the allocation of public numbering resources for commercial call services. Starting October 17, 2026, all companies making commercial calls will be required to use this new prefix, allowing users to easily distinguish between personal and commercial calls.

## What remains unclear Despite the positive intention behind this measure, many users are skeptical about its actual effectiveness. Past experiences with similar initiatives have left doubts about whether prefix 400 will truly help reduce spam volume, or if it will simply become another number that users will have to learn to ignore.