One feature of many other handheld devices is the ability to use the device as a portable flash drive to move data between a couple of computers. The iPhone doesn't have that ability now, but will on July 28, 2008.
That's the day that DataCase will be available in the iTunes App Store for $6.99. From Veiosoft, DataCase works with Apple Filing Protocol (AFP) and Bonjour to allow any Mac on the same network as your phone to transfer files to and from it.
Your iPhone appears as a Mac volume, so you just drag-and-drop data you want to take with you. If you're a Windows or Linux user, DataCase gives you the same capabilities from your iPhone using HTTP and FTP.
In case you want to view those files you've moved to your iPhone, DataCase lets you read Microsoft Office, PDF, and text files. You can create up to 16 different volumes on your iPhone, each of which can be set up with read/write/browse permissions. Volumes can be made invisible to protect data from unauthorized people or iPhone snatchers.
This is an innovative app that I think a lot of iPhone owners are going to buy come July 28th.