I setup a VPN client on the 3G interface since there's no public IP address, and I connect to it from my own home network as a local IP address (which can't actually access my network due to explicit firewall rules I setup).

This way I can reboot the modem remotely even if the Internet is dead, and I also setup the Pi to reboot itself every night at 3am, in case something goes wrong and the VPN client crashes.