The link in the article has a lot more info: https://arstechnica.com/information-technology/2018/04/t-mobile-deceived-customers-with-false-ring-tones-on-failed-

The link in the article has a lot more info: https://arstechnica.com/information-technology/2018/04/t-mobile-deceived-customers-with-false-ring-tones-on-failed-phone-calls/ https://arstechnica.com/information-technology/2018/04/t-mob... The fastcodesign link doesn't really add anything except a story that's not quite accurate (saying it's the signal.. which is wrong).