https://www.bleepingcomputer.com/news/security/t-mobile-discloses-data-breach-after-sim-swapping-attacks/

American telecommunications provider T-Mobile has disclosed a data breach after an unknown number of customers were apparently affected by SIM swap attacks.

SIM swap fraud (or SIM hijacking) allows scammers to take control of targets' phone numbers after porting them using social engineering or after bribing mobile operator employees to a SIM controlled by the fraudsters.