There’s been quite a bit of talk out there about a new iPhone app called NetShare (iTunes Store link). The app allows you to use your iPhone as WiFi base station, “tethering” your Mac to the iPhone and using its 3G Internet connection. In essence, you can connect your Mac to the ‘net wherever you can get a 3G signal; your iPhone becomes a cellular modem.

This app is controversial because the mobile carriers obviously don’t want you to use it. There are Internet apps on your computer, like torrent downloading, voice and video chat apps, and other high-bandwidth programs that could seriously strain their broadband services. Some believe that AT&T’s contract forbids the use of such an app, which is the reason many believed Apple took it down from the App Store yesterday–except that now the app is back up.

Interestingly, NetShare is listed on the Japanese App Store, but when I try to see the app’s details, I get a message saying it’s not currently available; if I click on the “Buy App” button, I get prompted to enter my password, and because I don’t really want to buy it (I don’t really need to, and it’s ¥1200), I can’t see if the purchase would actually go through (I am guessing not).

But if you have access to the U.S. App Store, if you could really use this app, and you are willing to risk the wrath of your carrier for over-using the supposedly unlimited data plan you paid for, then you should buy it before Apple changes its mind again and takes it off the market.

Update: Too late, it’s off again. Any bets as to whether it’ll come back?