not an new issue the whole point of ss7 is interconnectability
so a caller on joe bobs telephone network can call yuri's cell phone in moscow which transverses many copper networks and finally to a cell tower. When you place a call, until the dial tone hits your ear ss7 is setting up the connection.
Any opinions expressed by me are mine alone, posted from my home computer, on my own time as a free American and do not reflect the opinions of any person or company that I have had professional relations with in the past 59 years. meep