Yes, you can. Sixfab SIM can be used in the Sixfab CORE solution. Note that Sixfab CORE only supports Sixfab SIM. When using a different SIM, the user guides regarding the internet connection should be followed from the product page of the module you have.
To use the UART follow the steps mentioned in the UART guide. Only Quectel modules are compatible with the UART of the HAT, Telit modules are not compatible.
Technically, the Sixfab Base HAT in the KIT is a bridge between the mini PCIe module and the Single Board Computer (SBC). Compatibility between the mini PCIe module and SBC depends on the kernel, OS, and driver support.
For instance, all Quectel and Telit modules in the KIT are Linux compatible. If the kernel of Linux doesn't contain the drivers by default, you can follow the Linux Driver guides provided by each OEM.
The HAT is compatible with all Raspberry Pi which contains a 40W GPIO header.
Updated about 1 month ago