http://news.yahoo.com/s/ytech_gadg/20100602/tc_ytech_gadg/ytech_gadg_tc2354

AT&T just did away with its all-you-can-eat smartphone data plans — bad news for those who stream video on their iPhones all day, but potentially good news for the rest of us, given that the cheapest of the new capped plans goes for just $15 (rather than $30) a month. Also: AT&T is finally ready to offer iPhone tethering.

First, a little background. Up until now, AT&T was charging all of its smartphone customers — including iPhone users — $30 a month for unlimited data usage. Starting Monday, June 7, the unlimited data option will be going away for new subscribers, to be replaced by two cheaper, capped plans. (If you're currently on an unlimited AT&T smartphone data plan, you don't have to switch to the new, capped options, which are required for new subscribers only. But AT&T says you can opt to make the switch without extending your contract.)

DataPro: Heavy smartphone users will probably opt for this $25-a-month plan, which offers up to 2GB of data a month at a $5 savings over the current unlimited plan. If you go over your 2GB monthlyallotment, AT&T will charge you $10 for an additional gigabyte. No, overage charges are never fun, but it's certainly better than typical per-MB overage rates, which result in those catastrophic $50,000 cellphone bills you see on CNN.

DataPlus: A $15-a-month option that offers 200MB of monthly data, good for (as AT&T puts it) 1,000 e-mails without attachments, plus 150 messages with attachments, plus 400 Web pages, plus about 20 minutes of streaming video. If you crack the 200MB monthly cap, you get another 200MB for $15. 

So, which plan is right for you? That depends on how much data you're using a month, which you can typically check on your smartphone's settings menu (for the iPhone, tap "settings," then "general," then "usage," then scroll down to the "cellular network data" heading).

I consider myself a pretty heavy iPhone user, so I was leaning toward the $25-a-month DataPro plan. But to my great surprise, I found that I'd used barely a gigabyte of AT&T 3G data in the past seven — count 'em, seven — months, or about 133MB of data every 30 days. I guess that means I do the majority of my iPhone browsing and streaming over Wi-Fi. So I just might switch to DataPlus rather than to DataPro. I'd save $15 a month over my current $30-a-month unlimited plan, give or take the occasional overage charge.

To help keep track of your data usage, AT&T says it will send you up to three text-message warnings when you approach your monthly cap: when you've used 65 percent of your data, then 90 percent, then when you've run dry. You can also check your data usage using the myWireless app for the iPhone or by calling *DATA#.

What about those $30-a-month unlimited prepaid plans for the iPad? They're going away too, unfortunately, to be replaced by the $25-a-month DataPro plan — and that's a bummer, considering the iPad's aptitude at streaming video. But at least AT&T is offering up free, unlimited use of its 20,000 Wi-Fi hotspots.

Last but not least: Almost a full year after Apple first announced that the iPhone would support Internet tethering, AT&T is finally set to offering a tethering plan for U.S. iPhone users (starting "when Apple releasesiPhone OS 4 this summer"). Welcome news, but keep in mind that you'll fork over $20 a month extra to tether your iPhone (via USB or Bluetooth) to your laptop. 

Overall, I have to say that I'm disappointed to see AT&T dumping its unlimited data plans, especially for iPad users — and don't be surprised if the other big U.S. carriers follow suit. Then again, depending on how much data you use on your smartphone, you actually might end up saving money on a cheaper, capped plan without feeling a thing. Indeed, based on my surprisingly low monthly data usage, I might fall into the latter category.

What do you think? Happy with AT&T's revamped data plans? Bummed that the unlimited plans are going away?

• AT&T: News release