What is a GSM compatible SIM card? Mobile devices use SIM cards to connect to cellular networks. But not all SIM cards are the same. GSM SIM cards are special. They let devices work on GSM networks, which are used all over the world. learn more: https://medium.com/@callcentersolutionccs/what-is-a-gsm-compatible-sim-card-e75444538c02 #gsmgateway #simcard #gsmnetwork #gsmdevice