ModemManager does not detect carrier lock
I have a ZTE MF821 USB 4G stick. ModemManager detects it fine, but when trying to connect it fails with gsm-network-timeout. --3gpp-scan returns a failure.
When I plug it into a Windows computer, using its built-in software, after asking for PIN it detects it's carrier locked and asks for a MEP unlock code. ModemManager should detect a carrier locked device, and display an appropriate error, even if unlocking it is too device-specific.