Saw 2 threads on this issue. Neither has a solution.
Keyboard sounds while dialing
hxxp://forums.crackberry.com/f61/keyboard-sounds-while-dialing-3521/?highlight=dialing
HELP! Turn off sound when dialing phone 8830
hxxp://forums.crackberry.com/f61/help-turn-off-sound-when-dialing-phone-8830-a-1655/
It's been awhile since both posts so I was wondering if anyone has found a solution or if the newer firmware has added an option to turn off this annoying 'feature'.