I use a Sierra Aircard on my Kubuntu 8.04 netbook. When I received it the Aircard had already been programmed by Sprint with my user name and password. I used the Windows Sprint connection software to figure out the phone number that it calls to connect to Sprint. That number is exactly this:
Then I used KPPP to connect to Sprint under Kubuntu. You don't have to fill in all of the fields in KPPP. Just fill in the ones that are necessary. Give the connection a name and give the #777 as the phone number, or whatever characters your ISP requires for your Aircard to connect.