What cellular hat to use?

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?

Hi @ralph ,

The back up for broadband should be 4G connection which can be obtained using our Raspberry Pi 4G Cellular Kit. On the other hand, there are options of CAT M1 HAT, a low power wide area cellular technology that is built specifically for IoT projects. It is suitable for low amount of data.
These module are used over the USB hence the UART will be free.