BeagleBoneBlack+mikrobus_cape+GSM2

Hi, since a few weeks I got my BBB plus a Mikrobus cape (4 slots) plus a MikroElektronika GSM2 modem.
I was able to run it using minicom only: getting phone calls ans sending sms.
I tried to manage it from java comm packages (jSSC, purejavacomm, etc.).
No way and no errors: I simply get back the command I just sent out, even a simple “AT”.
No matter echo setting, it looks a kind of shortcut.
Thanks for any help, I’m running short of ideas.

Renzo