WWAN module for servers

[Fabian Schörghofer]

That's because there are no "plain" PCIe devices for this.
All cards are USB devices which use the USB pins present on the mpcie or 
m.2 connector. I think Sierra Wireless EM7565 has a PCIe mode, but you 
still need USB to configure that and there are no drivers for it (yet).

So your best bet would be to buy a laptop card and use the adapter you 
already found. Connect to either an internal USB port, or to USB headers 
on your mainboard. Normal PCIe ports on your mainboard don't include USB 
pins.