Telekom introduces “Call Check” as a warning system against telephone fraud

Deutsche Telekom introduced a new warning system against fraudulent phone calls in December 2025. The function, called “Call Check”, is activated on the Telekom mobile network and is aimed at all of the company’s customers. The aim is to alert users to an increased risk of fraud as soon as they receive a call and thus reduce damage caused by telephone fraud.

If a call is received from Germany or abroad and the associated phone number is classified as dubious or fraudulent in a database used by Telekom, a clear warning appears on the smartphone with the text “Caution, possible fraud!”. The decision to accept or reject the call remains entirely with the called party. There is no automatic blocking or blocking. The technical implementation takes place directly in the Telekom network; no additional app or manual activation by the customer is required.

The approach follows the principle of pure information. Telekom uses known and reported fraud numbers, which are continuously updated. The aim is to identify classic scams such as fake competitions, alleged surveys or calls aimed at obtaining bank details, access data or passwords at an early stage. The effectiveness of this depends largely on the up-to-dateness and quality of the underlying telephone number lists. Consequently, the absence of a warning does not necessarily mean that a call is legitimate.

Telekom is not alone in the German mobile communications market in taking this step. Vodafone already activated a similar warning system in May 2025. According to the company, this system has triggered around 50 million alerts since its introduction. Internal evaluations by Vodafone show that only around twelve percent of calls flagged as suspicious were nevertheless answered. In contrast, the acceptance rate for anonymous calls without a displayed telephone number is significantly higher. It is also noticeable that in the vast majority of cases, pre-identified fraud calls were terminated after less than 30 seconds, which suggests that callers were more cautious.

The third major mobile network operator in Germany, Telefónica Deutschland with the O2 brand, has not yet introduced its own network-based warning system of this type for its customers. This means that the protection mechanisms against telephone fraud currently differ significantly between the networks.

Conclusion

With the introduction of “Call Check”, Deutsche Telekom is significantly expanding its preventive measures against telephone fraud in mobile communications. The system focuses on transparency instead of automatic intervention and strengthens the basis for users’ decisions in a situation in which fraudsters are increasingly operating professionally and internationally. Vodafone’s experience suggests that such warnings can measurably influence the behavior of those called. Nevertheless, vigilance remains necessary, as not every fraudulent call can be detected and a lack of warning does not guarantee seriousness.