T580 upgrade and WWAN Slot SSD finding : r/thinkpad
SSD in WWAN slot? : r/it
Mini PCIe WWAN Card to USB Adapter with SIM Slot, Mini PCI Express WWAN/LTE/4G Module Tester Converter, Support 30mm 50mm Wireless Wide Area Network Card
Apparently T480s can boot directly from WWAN Slot! : r/thinkpad