You’ll need to supply the developer of the app with an identifier for your device so that they can give it permission to run the application. The developer will then send you two files that are required to run the app: a provisioning profile and the application itself. You can either use the Ad Hoc Helper app to send your Unique Device Identifier (UDID) to the developer or follow these steps:

1. Connect your iPhone, iPod Touch, or iPad to your computer.
2. Open iTunes if it isn’t already.
3. Select your iPhone, iPod Touch, or iPad from the Devices section of the list on the left side of the iTunes window.
4. Select the Summary tab.
5. Click on the Serial Number field to the right of the large icon of your device. It will change to an Identifier field.
6. Press Command-C (Macintosh) or Control-C (Windows) to copy the identifier to your clipboard.
7. Paste the identifier into a message to the developer by using Command-V (Macintosh) or Control-V (Windows).

Once you’ve received both files from the developer, follow these steps to install an app that is distributed in an ad hoc fashion instead of via the App Store.

1. Connect your iPhone, iPod touch, or iPad to your computer.
2. Drag the provisioning profile file to iTunes (it has a .mobileprovision extension). You won’t receive any feedback from iTunes that this was successful.
3. Decompress (or unzip) the Zip file containing the app. You’ll use the app file contained inside the Zip for the next step.
4. Drag the application file (it has a .app extension) to iTunes.
5. Sync your iPhone, iPod touch, or iPad. If the app does not appear on your device, make sure it is one of the checked apps on your device’s Applications tab in iTunes before syncing.