Hi Matt,
I thought I'd come on and offer my 2 cents on this. I have a Dell XPS M1330 though without the 3G modem built-in like yours. It definitely sounds to me that the modem is conflicting with the USB dongle. If you ordered yours with the modem then you might be able to use that with the laptop instead of the dongle (just a thought!). In either case I'd recommend you check the
Dell support page to see whether there is any software you can download to either enable or disable the hardware. I'm fairly certain I've seen something floating about their site.
All you do is enter your Service Tag found on the underside of the laptop and you can check what software is available. If we can establish whether you can disable the modem or indeed make use of it for the purposes of VMC I'm confident we can get you up and running
Keep me posted!
Adam
eForum Team.