What is the relationship between 4G Cellullar Module and SIM cards?

1.4G Cellullar Module is a kind of remote sollution provided by ECOVACS that is built into the Cellullar Module. If your home has no Wi-Fi or the Wi-Fi signal is poor, you can achieve remote control from 4G Cellullar Module .
2.You must buy a SIM card and insert the Cellullar Module after activation it.