Specifically, which SIM card do you have? There are several commands you can use to monitor your network. You can start with ifconfig. More information on ifconfig here 15 Useful "ifconfig" Commands to Configure Network Interface in Linux . Also I’ve found this link which discusses ways of monitoring Linux performance 20 Command Line Tools to Monitor Linux Performance . Some of these methods will not work right away and might require you to install additional packages.
Also, take a look at mini PCI express 3g card? you might find it helpful.