All of our products larger than 9.7inch support a 4G module but it is not mounted by default.
The 7” A7 products don’t support a 4G module because there’s not enough space on PCB for it.
4G module is optional. Different countries use different 4G modules so it is up to you to choose an optional 4G/LTE while ordering. Just check the box and it will be added to your order. If you do not want the board to be delivered with it, you can add it later. What you need to bear in mind is that the 4G module you want to add matches the onboard connector.
Different 4G modules have different pin definitions.  Besides the hardware compatibility, you will need to port the driver.  You can always contact us in case you need any assistance doing that.