I am using the built in GSM (UMTS) modem of my Thinkpad X1 extensively because I am often in places with flaky internet connections. I connect through the standard Network Manager on Ubuntu and everything works fine. There was one major annoyance though. Every time I wanted to top up the SIM balance or book a new package, I needed a phone to send and receive USSD codes. So I took some time to figure out how to do it from the shell. I wrote this down as a help for others and a reminder for myself. Without further ado...
First intsall gammu and picocom.
➜ ~ sudo apt-get install -y gammu picocom