When mmcli, which was passed a USSD-related option, detects that a modem needs to be unlocked, it prints out a terse "modem not unlocked yet" message. It doesn't indicate what kind of "unlocking" is needed, leaving the user confused and unable to remedy the problem (--help-all output doesn't even contain the word "lock"); and this is even though mm_modem_get_unlock_required() returns this very information (cli/mmcli-modem-3gpp.c). Additionally, unlocking is reportedly not needed at all for at least some modems, despite ModemManager claiming otherwise: <https://stackoverflow.com/revisions/31864567/2>
Thanks for the report. This bug was actually a leftover from commit 001f35234e16d7aeb2ed1282ba3b57aea73c5a9e, and has been there for 4 years now... I've pushed a fix to git master, mm-1-6, mm-1-4 and mm-1-2.
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