Its also been a problem in Australia, Optus (2nd biggest teleco) used to allow number porting or activating sim against an existing account with a bare minimum

Its also been a problem in Australia, Optus (2nd biggest teleco) used to allow number porting or activating sim against an existing account with a bare minimum of detail - Like a name, address and date of birth. If you had those details of a target you could clone their SIM and crack any SMS based MFA.