Two things I learned about the Novatel USB760 is that (1) you want
USB_ModeSwitch http://www.draisberghof.de/usb_modeswitch/ installed (it comes with Slackware 13.37 by the way) and (2) you need to use it with
KPPP.
My experience with actually using the thing was that every so often I needed to unplug, wait a bit and replug before it would connect (I do live in the boonies where cell service can be iffy and have changed over to HugestNet -- where satellite service can be iffy sometimes too but there you are).
So, if you don't have
USB_ModeSwitch installed that may be the simple fix.
Hope this helps some.