https://www.techdirt.com/articles/20190513/09071542199/att-verizon-employees-caught-up-doj-sim-hijacking-bust.shtml

Wireless carriers are coming under increasing fire for failing to protect their users from the practice of SIM hijacking (aka a port scam). The practice involves posing as a wireless customer, then fooling a wireless carrier to port the victim's cell phone number right out from underneath them, letting the attacker then pose as the customer to potentially devastating effect. Last year, a customer sued T-Mobile for failing to protect his account after a hacker pretending to be him ported out his phone number then stole thousands of dollars worth of cryptocoins.

Subsequent reports have shown how identity thieves use SIM hijacking to do everything from cleaning out bank accounts, to stealing valuable Instagram usernames and selling them for Bitcoin. Reports often showed how these scams were being helped with the willful help of some cellular carrier employees, something wireless carriers haven't (understandably) been particularly keen on talking about.