the race was on to be the first to connect a regular PCIe expansion card to a Raspberry Pi 4 SBC. Now [Zak Kemble] has created a new approach, using a bridge PCB that replaces the VL805 USB 3 ...

These modems would often slot into a Mini PCI-e slot ... run that off the USB port. Then, it’s a simple enough matter of figuring out which pins are used to talk to the SIM card, and soldering ...