If you own a laptop (Dell, HP, Lenovo) with a WWAN module, it is very likely that the modules are FCC-locked on every boot, and the special FCC unlock procedure needs to be run before they can be used.
Until ModemManager 1.18.2, the procedure was automatically run for the FCC unlock procedures we knew about, but this will no longer happen. Once 1.18.4 is out, the procedure will need to be explicitly enabled by each user, under their own responsibility, or otherwise implicitly enabled after installing an official FCC unlock tool provided by the manufacturer itself.
If you want to enable the ModemManager provided unofficial FCC unlock tools once you have installed 1.18.4, run (assuming sysconfdir=/etc and datadir=/usr/share) this command (*):
sudo ln -sft /etc/ModemManager/fcc-unlock.d /usr/share/ModemManager/fcc-unlock.available.d/*
The user-enabled tools in /etc should not be removed during package upgrades, so this should be a one-time setup.
(*) Updated to have one single command instead of a for loop; thanks heftig!