Advanced Configuration Tool for Windows Phone is a home brew app from Julien Schapman. This app lets you to customize themes, sounds, tiles, icons and to tweak your Windows PhoneÂ such as 3G toggle switch visibility, etc,. The app is is currently compatible with HTC, Samsung and LG Windows Phone devices. The new version 126.96.36.199 supports Windows Phone Mango and more stable than previous releases.
You can find more details about this app here.