iPhoneHome is an app available in the Installer.app through the Ste Packaging source. This is an app that allows you to change the double tap feature of your home button. In the Settings on your iPhone under general there is a setting for your home button…you are given three option to change it to on a stock iPhone; Home, Phone Favorites and iPod. iPhoneHome allows you to change the double tap feature to any app on your iPhone or even a phone number or blank email. When you open the app you get a screen that has two options Change App and Save & Quit. Just tap Change App and it will bring up a scroll wheel of all the apps on your iPhone. Just tap on the app your would like to set as your double tap and tap Save & Quit. Your iPhone will reset and now when you double tap the home button it will take you to the app you selected.

http://appleiphoneschool.com/iphonehome/