This is a primer on how to install software sent to you by a developer.  This process is called “ad hoc distribution”, and it’s Apple’s way of allowing developers to send pre-release software to up to 100 users. 

1.  You should have already sent the developer your device ID.  If not, follow these instructions, and wait for the developer to send you an application configured to run on your device. 
2. Unzip the file sent to you by the developer.  You’ll see two files, one that ends in “.app”, and one that ends in “.mobileprovision”.   (On Windows, the “.app” unzips to be a directory, but carry on as if it were a file.) 
3. Open iTunes and attach your iPhone. 
4. Sync your iPhone.  
5. In the panel on the left, click on Applications, under the Library section.  
    
   
    
6.  Drag the “.app” file and the “.mobileprovision” file to the Applications window. 
    
7. Sync your iPhone again. 
8. You’re ready to start Beta testing!