Volume Boost boosts your iPhone speaker volume.
Volume Boost is a Cydia App that works only on jailbroken iPhone and supports firmware 2.2, 2.2.1 & 3.0.
Installing Volume Boost
The installation is very straightforward. Simply launch Cydia and search for “Volume Boost”. The application requires Winterboard for activation. So if you do not have Winterboard, Cydia will also install it for you.
After installation, Cydia will automatically reboot your iPhone. To enable volume boost, launch Winterboard and tap on “Volume Boost 3.0?. Then click HOME button to activate the volume boost. You’ll have to wait for 20 – 30 seconds for Winterboard to refresh.
From my test on iPhone 3.0, the Volume Boost only increases the speaker volume slightly but it does boost the volume of your headset. If you experience speaker volume issue, try to test this out and let us know if it works for you.