Yes it can be done very easily both for inner and outer speaker volumes.
You need a bunch of software and the link to a webpage which i've already posted but i'll post again.
It has instructions to do alot of things to your phone like changing colour schemes and such.
The webpage explains how to do all this in great detail, but i had great problems using the program (p2kman.exe) under Win98Se. Worked a charm under Xp though.
http://home.planet.nl/~viss3662/V525/hex.html
Let me know how you get on
Regards
Alias