Beginner question: I need a cellular modem, to connect a Raspberry Pi zero. Requirements: Needs to use little or zero power when off. No need for voice calls or SMS, only to occasionally bring up a data connection: It is used as an emergency backup when normal broadband fails. The easiest way to do this is probably to bring up a PPP connection over cellular when needed. I would like to keep the UART on the Pi free, so connecting via USB would be ideal. There are plenty of Pi GPIO pins I can us for power control/monitoring on the cellular hat. It has to work right here in California; ideally with a Google Fi data-only SIM (which implies T-mobile’s network). Bandwidth requirements are minimal … when in use, I need to get a few kB in and out in a few seconds. But if I can get good bandwidth once in a while (megabits), that wouldn’t hurt, then the device could do double duty as an emergency access point. I don’t need extra relays or 1-wire connections, nor GPS. The device will be installed outdoors, in a weathertight box, with an external small antenna (via uFL adapter cable).
I had planned to use the Adafruit FONA for this (because it is physically small, and cheap), and prototyped with it, but then T-mobile dropped 2G support, so that option has vanished.
Sixfab makes three different models: The $69 “Cellular IoT hat” (which does LTE-M and NB), the $89 NB-IoT shield, and the $99 Cellular IoT application shield. Other than the obvious absence of relay/sensors, do I care about the differences? Can I just go with the cheapest one? I wonder whether the different types of LTE (like M1, NB and eGPRS) make a difference to me. And: What version to order? Worldwide, or America/Verizon?