Quectel EC25 + Sixfab LTE hat + Rpi OS Trixie + Rpi4b + ModemManager + NetworkManager

Steps

1. Install Rpi OS with rpi-imager
2. Connect hat to Rpi, insert sim (disable pin from a phone first)
3. Start Rpi, login, then in term or console :

NetworkManager + ModemManager setup

Here are the only relevant commands here :

mmcli -L
# gets you /org/freedesktop/ModemManager1/Modem/X where X is your modem id
sudo mmcli -m X | grep 'primary port'
# gets you your ifname (e.g; cdc-wdmX)
sudo nmcli connection add type gsm ifname cdc-wdmX con-name FOO apn BAR user BAZ password QUUX
# use your ifname, and your carrier's APN settings for apn, user, password
sudo nmcli connection up FOO
# activate connection

See here : [https://wiki.archlinux.org/title/Mobile_broadband_modem#ModemManager] and here : [https://wiki.archlinux.org/title/NetworkManager#Mobile_broadband_support]