L’ International Mobile Subscriber Identity (IMSI) est un numéro unique, qui permet à un réseau de téléphonie mobile de type GSM, UMTS ou LTE d'identifier un usager. fr:International_Mobile_Subscriber_Identity

Presenting QCSuper: a tool for capturing your 2G/3G/4G air traffic using rooted Qualcomm-based Android phone.

and produce a PCAP analyzable using Wireshark and more. https://labs.p1sec.com/2019/07/09/presenting-qcsuper-a-tool-for-capturing-your-2g-3g-4g-air-traffic-on-qualcomm-based-phones/

OR Dummies style

 tshark -i lo -Y "e212.imsi" -V 2>&1 | sed 's/^[ \t]*//;s/[ \t]*$//' 2>&1 | grep "IMSI:"