Majors: 1. Renting access by pretending to be legit telecom business 2. Internal access 3. Internet hacking into less protected telecom operators to then com

Majors: 1. Renting access by pretending to be legit telecom business 2. Internal access 3. Internet hacking into less protected telecom operators to then compromise the SS7 core network nodes and send traffic from there. Other ways exist, but these represent the bulk.