Yo just a heads up.
SS7 vulnerabilities aren't about free phoning or whatever you imagine. It's about being able to track phones, read and redirect calls/sms.
Also I love how Granger is biased when he describes his vulnerabilty vs anything else.
Some extra food, it's old but nice:
https://www.ted.com/talks/avi_rubin_all_your_devices_can_be_hacked