I was having a bunch of trouble with my Vodem for the last few weeks. Particular when I was using it a bit further away from the CBD, it seemed to be very unstable while being connected to the network and it seemed that it had some issues when it tried to switch between the 3G and the 3G Broadband network.
The symptoms were that the connection was physically still established, but basically it was not possible to get to any host. The only solution then was actually to pull the Vodem from the USB port, give it a few seconds, put it back it, launch the Vodem software and reconnect. After that happened to me various times IN the CBD I was annoyed enough to actually figure out that Vodafone has release a new version of the Mac OS X software for the Vodem: 2.07.03.00. I’ve installed it last week and since then – no issues anymore. It still sometimes flicks back and forth between 3G and 3G Broadband, but it hasn’t lost connection ever again when trying to get back to 3G Broadband