The difference between Volume Amplifier and other Voice boosting tweaks out there on Cydia is that it does not alter a specific OS configuration file (which actually don't work), it actually manipulates the audio stream in such way that you will really notice the difference.
We posted detailed instructions on how to install Volume Amplifier when it was first released. You can follow those instruction here.
What's New In This Version:
● Now amplifies EVERYTHING ! now you can amplify your iPod music, VOIP calls (such as Viber & Skype), Radio players, Ringer and much more.
● On iPhone 4S it only amplifies audio that comes out of the external speaker.
● Added support for iPhone 4S.
● iPhone 4 & 3GS won't be supported because of technical issues. ever. sorry.
You can purchase Volume Amplifier from Cydia for $1.99.