Building 4G/LTE Router

[msplsh]

IDK how you're going to get a PCIe LTE modem on USB to work without a SIM slot.

 

[balanga]

https://www.ebay.co.uk/itm/Mini-Wireless-PCI-E-to-USB-Adapter-with-SIM-8Pin-Card-Slot-for-WWAN-LTE-Module/142650904466?hash=item2136a80f92:g:WuIAAOSw3q5aVIQo

 

[JohnnySorocil]

That is the exact model I have (well, two, one was donated to a friend who is using it) and works for something like 4 years now. Only annoyance is flimsy USB connector.
LTE modem is basically a USB UART device (I got 3 of them, one is modem, 2nd one is ???, 3rd should be GPS).
mPCIe slot (in older laptops) can have various pinouts (for use with mSATA, LTE, WLAN cards...) but one configured for WWAN modem is almost a breakout board for USB and SIM pins: https://hackaday.com/2017/03/29/use-a-mini-pci-e-3g-card-with-usb-instead/

I have ordered M.2 adapters (newer layout for addon cards for laptops) and LTE modems but didn't try that but it should be the same (only different physical connector).

Edit: I cannot guarantee that every mPCIe LTE modem out there is USB -> 3x UART device, but I can guarantee that the one I got is (Dell DW5550 by Ericsson)