There are some hidden options which you have to enable via modifying some file. (see here and here.)

Enable a feature

For this you have to have ssh-access enabled!!

1. ssh into the iPhone (remember: the root-password is alpine)
2. cd to /System/Library/CoreServices/Springboard.app/
3. run this command: plutil -c xml1 M68AP.plist (this will convert the binary-XML to plaintext)
4. now use nano, mcedit or vim to edit the file
5. find the capabilites dictionary right at the top of the file
6. add the following two key/value-pair:

<key>gas-gauge-battery</key>
<true/>

1. save the file
2. run plutil -c binary1 M68AP.plist to convert the file back into binary-XML format
3. logout
4. reboot(=respring) the iPhone

Features Explained

accessibility

This will add a new settings menu below General (right below International). It is empty on iPhone 3G.

gas-gauge-battery

This will enable a new setting under General → Usage to enable a percentage field left of the battery icon.

video-camera

This will enable a new photo <=> video switch in the camera interface.

voice-control

This will add a new settings menu below General → International. It is empty on iPhone 3G.

More Features

In the file /System/Library/PrivateFrameworks/GraphicsServices.framework/GraphicsServices there are various more feature codes listed – here’s a screendump:

...device-name-localized...device-name.still-camera....cameraRestriction...telepho
ny...sms.video-camera....auto-focus-camera...wifi....accelerometer...magnetometer.
...gps.location-services...microphone..opengles-1..opengles-2..volume-buttons..rin
ger-switch...piezo-clicker...bluetooth...unified-ipod....youtube.youtubePlugin...g
reen-tea...not-green-tea...international-settings..stand-alone-contacts....delay-s
leep-for-headset-click...launch-applications-while-animating.load-thumbnails-while
-scrolling.sensitive-ui....apple-internal-install..all-features....nike-ipod...app
licationInstallation.voice-control...proximity-sensor....gas-gauge-battery...acces
sibility...mms.encrypted-data-partition....encode-aac..fcc-logos-via-software..tel
ephony-maximum-generation....hiccough-interval...application-display-identifiers.t
v-out-settings.screen-dimensions...main-screen-width...main-screen-height..main-sc
reen-scale...main-screen-orientation.explicitContentRestriction..volume-limit-rest
riction....inAppPurchasesRestriction...enforce-shutter-click...enforce-googlemail.

Anyone tried nike-ipod or enabling the magnetometer on a 3G? Also what could green-tea be?