Ok, here we go again.
I managed to get the Huawei E3131 running with sakis3g and wvdial. The trick was to use usb_modeswitch with the following mode ID:
sudo usb_modeswitch -v 12d1 -p 14fe -V 12d1 -P 1506 -M “55534243123456780000000000000011060000000000000000000000000000”
The modem is now switched to:
Bus 001 Device 005: ID 12d1:1c05 Huawei Technologies Co., Ltd. E173s 3G broadband stick (modem on)
It is up and running for the last 24h hours without any problems.
@eblex I think for the future we will run the modem with your solutions and the brand new resinOS 2 with NetworkManager
Thank you all for your great help! If someone is in trouble to get his modem running, just ask me.
Cheers,
Matt