I would like to share my knowledge on which devices is supported by RPI or not.
I have been using ZTE MF821D for a long time, and this one is really great and reliable. But there is one drawback.
If this modems loses signal , there is no way to establish link again without unplug or reboot RPI.
For some reason the modem (/dev/cdc-wdm0 ) disappear from the source list.
So i wanted to test another modem, and today i got Huawei E3276 4G LTE Cat. 4.
This modem works almost out of the box. This device won’t work with UQMI but works with sakis3g or wvdial, also reconnecting if loss of signal works perfect, and that is a great feature.
I will create complete installation procedure for Huawei E3276 4G LTE Cat. 4 soon. I will encourage you to post any knowledge you might have about supported and un-supported devices.