The application basically turns your iPhone into a portable Wi-Fi hotspot, giving all of your Wi-Fi-enabled devices internet, wherever you have a cell signal. There are similar solutions available for iPhone users who have jailbroken their handsets, but they are significantly more complicated than Nullriver's offering, and since they require a hacked phone, don't hold mainstream appeal.
Those of us who were not quick enough to grab the app while it was available on the App Store seem to be out of luck for now. Links to the application now pop up with an error message that reads, "The item you've requested is not currently available in the US store." It's not exactly clear what happened with NetShare, how it slipped through the cracks, or why it was pulled. The app may have accidentally gotten through in the avalanche of new applications that are being added to the store, however it seems unlikely that someone at Apple would have signed off on this app, not knowing what it did. It would appear that either Apple, AT&T, or both had cleared the application, then quickly reconsidered. Apple has not yet responded to a request for a comment on the issue.