Seems like this is a hard issue for everyone switching over from windows. For those of you like me, who have have hell installing a 3g card on Linux, I have found a solution that works. For Sprint, anyway...
According the Sprint site, you stick the card in and run the command: "sudo mobprobe usbserial vendor=[xxxx] product=[xxxx]". The problem, is that for many cards this will not work(like the Novaltel U727, for instance; my card), as it was based on older versions of Linux. So here's the solution for newer cards.
Stick in your card, restart your comp in Linux, then go to Terminal and type in "sudo modprobe option". It will move down a line. Now go to network connections, your connection shouldl be listed. Click to connect. It takes two seconds. Too easy, eh?
BTW: run the card on Windows first, with a MicroSD card if possible. That a way, all your settings will automatically transfer over to Linux and you can just connect without setting anything up.