Have you unlocked your phone and noticed that the volume is very low? Audio has been a problem on the iPhone up until firmware v 1.1.1 which apple seemed to address in the update, but not everyone is able to upgrade to 1.1.1 yet. Below is a guide to increase your volumes just like the 1.1.1 firmware update.

Things you’ll notice:
1). DialPad is louder
2). Speaker, Ringtone, Headset, Receiver, Speakerphone volumes are noticeable.
3). System Sounds are louder
4). YouTube video sounds are louder

Test Experiment: (Thanks stlcaddie and ReVan)
If you want to see a difference download beatphone.app listen to the pads with the volume all the way up and then apply the modded files. Now go back to the beatphone.app and listen to how loud the pads are now.
Install Instructions:

1). Download this file: iPhone Volume Fix
UPDATED file: iPhone Volume Fix with softer dialpad
2). Copy the com.apple.celestial.plist file to /var/root/Library/Preferences (Delete the two files FIRST don’t just copy them onto the phone and select the option of overwrite.)
3). Copy the SystemSoundMaximumVolume.plist file to /System/Library/Frameworks/Celestial.framework/
4). Goto Settings > iPod > (switch off: Sound Check)
5). Reboot your iPhone.

UPDATE: If you do not notice a difference try:

1). Download

http://www.megaupload.com/?d=1SHSE3IF

put it into: private/var/preferences

2.) Reboot