To use a 3G broadband modem, install gppp with synaptics package
manager. When I installed 10.04 gppp was installed by default.
usb-modeswitch will switch the memory device on many usb modems. this
application, also listed in your package manager, removes the need to
eject the memory device most likely labled with the name of your phone
service provider.

If the memory on your device is mounted as a cd on your machine then you
will need to eject that image before you can continue setting up the
modem. After you have ejected the memory your modem will show up as a
mobile broadband connection. when you select setup a new connection, it
will ask the questions that are needed for your connection. You will
find a list of providers, your provider is listed in that list, I
checked, so you will not need much info to connect. With my
broadband2go service everything was done for me on 10.04 by selecting my
provider from the list. It was a little more work using 9.10 but was
still fairly easy, with only ejecting the memory device being any
different between the two Ubuntu releases.

One more note, My device needed to be setup with the provider in
windows. After that setup it just works.