@DominikHoffmann
I am looking for a cellular modem with an Ethernet port. Ideally, it would not also be a cellular ⇄ Wi-Fi gateway.
RasPi 4.0 / 5.0 with miniPCIe or M.2 modem card
As I am in the U.S., it would have to be able to handle SIM cards from Verizon, AT&T or T-Mobile.
A M.2 card in an external case with USB port is working here at my site
well for around 100 €
The idea is to use it in a WAN failover configuration.
There are other modems or small routers that are capable to
connect to the LTE bands of us mobile providers but the real
compatibility is there not really guarantied. And on top with
the both named solutions you may be able to upgrade the
modem to newer standards.
miniPCIe
FIBOCOM NL668-EU MINI-PCIE MODEM (4G/LTE)
~50 €
miniPCIe to USB WWAN case ~27 €
M.2
Sierra Wireless AirPrime EM7455 ~20 € (used)
M.2 to USB WWAN case ~34 €
5G LTE
M.2 solution for LTE 3G/4G/5G ~48 €
RaspBerry PI Solution
RaPi Hat ~20 €
RaspBerry PI 4 B+ 2GB ~52 €