Every new release of Ubuntu seems to break something that was working on my systems, and it was no different with the 10.04 release of Ubuntu: my Huawei e169 mobile broadband modem, which can be used in Australia on the Optus, Vodafone and Virgin mobile networks, and in Europe almost everywhere, stopped working.
The device would appear in the filesystem, but no matter what I did, it refused to connect.
It's quite easy to fix this, in fact. Firstly, install the usb-modeswitch package:
sudo apt-get install usb-modeswitch
Then create the file /etc/udev/rules.d/75-e169.rules with the following contents: