How to Connect USB Flash Memory to My iPhoneby Marie Cartwright
You've got your iPhone in one hand and your flash drive in the other. Getting them to work together may seem daunting: The iPhone doesn't have a USB port, nor could it support one if it were connected externally. To get your files from your flash drive to your iPhone, you need to use your computer as an intermediary. Before you begin, have iTunes installed on your computer and the FileApp application installed on your iPhone (see Resources). This tutorial is applicable for both Mac and PC users.
Plug your flash drive into a free USB port on your computer. Open the drive to view your files. Leave this window open.
Launch iTunes. Plug in your iPhone with its USB interface cable. Once your computer has detected your iPhone, a listing for the iPhone will appear under the "Devices" menu in the left sidebar of the iTunes window. Select your iPhone within this menu.
Select the "Apps" tab at the top of the main iTunes pane (located just below the audio progress bar at the top of the window). Scroll down to find the "File Sharing" section. Select FileApp from the "Apps" list.
Return to the flash drive window opened in Step 1. Click and drag the files one at a time into the "Documents" list within the iTunes window. Once all the files have finished transferring, you can disconnect your iPhone.