If your GSM modem SIM Card is configured with a PIN a NetworkManager is constantly trying to ask for that PIN on every wake up… and this is quite annoying indeed. So the easy way to remove a PIN protection from your SIM Card under Ubuntu would be:
sudo apt-get install gsm-utils
sudo gsmctl -d /dev/ttyACM0 -o unlock sc all 1234
here 1234 is actually your SIM Card PIN to be removed.