I'd like to add a 3G/4G modem to the mix as the board does not have any USB ports only ethernet ports... Is there a PCI-e card I can use that will take a SIM and supports a lot of frequencies and providers. Or does someone have any better ideas here.

Thanks heaps for your help.

Not really. The RB433AH has mPCI slots, not mPCI Express which modems use.

I'd suggest replacing the board if possible with a more newer model that has a USB port and a mPCIe port.