If you are testing or previewing a new version of an application then the developer may send you what is called an “Adhoc” build of that application. This is a special build that can be installed directly on phones without having to be downloaded from the AppStore.

An Adhoc distribution comes in two parts – the application itself and a certificate that contains the UUID of your device. Usually the developer will provide both of these files in a single zip file for you to install. The instructions below show how to install an Adhoc application under Mac OSX. The steps for a PC are exactly the same.

1. 1) Extract the contents of the zip file to a folder. There should be two files (on PCs it may be one file and one folder).
2. 2) Open iTunes
3. 3) Drag the the two items from #1 into the “Library” section of your phone. Click “Yes” if prompted to overwrite.
4. 4) Go to the “Application” list of your iPhone/iPod sync settings in iTunes, and make sure the new application is selected for synchronization.