Now that 5G is available and offers much higher bandwidth it may be that you folks are interested in some new development I just came across reading EP magazine. There is a pretty handy solution for Pi4 in he form factor of a HAT put on top of the Pi4. It is described in detail at: EP article on 5G HAT fpr Pi4. Unfortunately it is all in German…
The HAT is produced by Atlantik Elektronik: ATE, price not yet available. The HAT cooperates with a Quectel Module name EM06 also offered by ATE. Currently I am not planning to use th HAT, I just wanted to let others know that such device is now available.