The (Ukraine) government and military were doing very clever signals intelligence. So, if they pick up a bunch of Russian numbers clustered in one place, they can figure out where the enemy troops are and attack them. So, the Russians eventually wise up to this and ditch their Russian phones, but they just can’t give up that itch to stay connected. So, they take those stolen Ukrainian phones, pass them around, and a bunch of guys call home from one number. Of course, the Ukrainians were still listening, and they intercepted those calls whenever they ping a Ukrainian cell tower. These conversations provided really important intelligence to the armed forces of Ukraine, and now there are also potential evidence for war crimes prosecutors.