I was able to make calls using my RPI 3 model B+, Huawei E153 GSM Modem, and minicom.
I can see that the cellphone I'm calling was able to answer my call (from my Pi). I plugged in my headphones to the RPI but I can't hear any sound. Even if I talk the other party can't hear me.
I should mention I connect to my Pi via SSH and that's where I run minicom and issue AT commands.
I wonder what else should I do?