For newer desktop linux, there is a component called ModemManager which may interfer with your development when using Gemalto Terminal or module product. Here are two tips to deal with it:

• Stop the ModemManger for now via

 $ sudo service ModemManager stop  

• Permanently disable it via

 $ sudo systemctl --system disable ModemManager.service 

After using one of the two commands, you can safely use minicom/picocom to access module COM port.