
I've not personally tried this, but this looks solid. Let me know how it goes out there.
HOW setup tethering for Blackberry Pearl (8100) on a linux machine (Thibaut's Blog).
Reminder that if you are connecting to AT&T you'll need to use the modem information below in the etc/chatscripts/blackberry conf (the entry above uses T-Mobile's settings)
Modem Initialization String: AT+CGDCONT=1,"IP","wap.cingular"
Dial-up Phone Number: *99#
Dial-up username/password:blank/blank
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