You should have Cydia installed on iPhone in order to install installous. Installous is a free app-installation tool that contains thousands of free apps in its repository just like itunes app store. The difference is, installous offers free apps that you have to purchase on itunes app store. In other words, Installous is a program that lets you install cracked apps the same way you install official apps. You can also use Installous to install iPhone apps from downloaded ‘.ipa files’ or ‘app files’ directly on your iPhone. Installous is not available in Cydia app store. It is hosted by its developers in its own installation source. Installous can be installed by adding the Hackulous source to the Cydia. Cydia and Installous can only be installed on jailbroken iPhones. Here is how to install Installous on iPhone.
The iDevices (iPhone, iPod touch and iPad) hacking that allows users to access to the entire Unix filesystem is called jailbreak or Jailbreaking is a process that gives a user read/write access to locked OS files on iDevices. Jailbreaking gives a user complete control over iPhone (and other iDevices) including customizing it and 3rd party apps installation. Jailbreaking is a hack to gains access to areas of the iPhone, iPod touch or iPad that users are not supposed to mess with. After that users can install 3rd party cool programs or unlock the handset for use with another cellular network. Lets talk about jailbreaking in detail.
Comex, the developer of JailbreakMe 3.0 is about to release the iPad 2 jailbreak. One of the beta testers of iPad 2 jailbreak via JailbreakMe has leaked the jailbreak. He was able to jailbreak iPad 2 by downloading a pdf file in mobile Safari on the iPad 2 which contains the exploit developed by Comex and will jailbreak your iPad 2, allowing you to access Cydia. This iPad 2 jailbreak is currently in beta version and will contain few bugs and will only work on WiFi models of the iPad 2. Safari has been reported to crash on your iPad 2 if you use this method. Better approach is to wait for Comex final official release.