I'm looking into options for using a Routerboard with Sprint in the US. They're a bit of an odd carrier, using bands 25, 26, and 41, so most LTE cards won't work. Looking at the wAP R (and a few other options), they have a SIM card slot. Two questions:

1) How does the SIM card interact with the LTE card? I used to see Mini PCIe cards with a built-in SIM slot and assumed they worked together at a low-level, but now I'm wondering if the OS sees them as separate devices and uses the SIM card device for authentication.

2) Any recommendations for Sprint LTE cards? Some googling led me to the AirPrime MC7355, but websites have said it's "for Dells," and I know vendors have made devices in the mini PCI(e) form factor that aren't actually compatible, so I figured I'd check on that.

To 1) this was never a problem
2) look at this:
https://wiki.mikrotik.com/wiki/Manual:Peripherals