First you will need to call your provider and asked for a BB Tethering Feature (BB as in Blackberry) Once they provision you with the feature go to Google.com and type in the search box: blackberry tether linux
The first result you get is for a BB Pearl. Same stuff so click on it.
Wth i'll just provided the link:Tethering With Blackberry Pearl On Linux [Thibaut Colar's Home]
Follow instructions and see how it goes for you.