The wiki for the device explains how to use it, but not how to start it automatically at boot. So, as a workaround, let it try starting it up every minute via cron.

Open cron, via web or through crontab -e and put the following:

 * * * * if [ "$(ifstatus wwan | grep '"up"' | awk '{print $2}')" != "true," ]; then ifup wwan; fi