• by Mark Walsh  @markfwal, June 2, 2010

Ahead of the expected launch of a new iPhone model next week, AT&T Wednesday announced a new set of data plans that eliminates its "Unlimited" offering. The carrier has also added a long-awaited tethering option for iPhone users.

The new data plans, which go into effect June 7, will start at $15 a month and are geared to mobile subscribers who don't consume a lot of data while heavier users will pay $25 a month plus more for each extra gigabyte they use. AT&T suggests that all but a small proportion of users could save money under the new tiered-pricing structure.

The plans work with any AT&T smartphone but current customers are not required to switch to the new data options if they renew their contract or switch to another smartphone. But if they do switch, they can't go back to their old unlimited plan. To avoid so-called bill shock, customers will also get help tracking and managing data usage with text alerts and a data calculator.

These are the AT&T mobile data plans:

DataPlus--The entry-level plan, providing 200MB of data for $15 a month. This would save $15 a month on the existing $30 monthly unlimited plan for the 65% of its customers who use less than 200MB each month. Users who exceed the limit could get another 200MB for an extra $15.

DataPro--The high-end plan, offering 2GB of data for $25 a month, with each additional GB over the limit costing $10. With only 2% of AT&T subscribers using more than 2GB a month, DataPro would become the equivalent of the unlimited plan for all but the very heaviest data users.

Tethering--Customer choosing the DataPro plan would be able to add tethering -- the ability to use smartphones as a modem to connect other devices to the Internet -- for an another $20 per month. (But the additional $20 doesn't buy more GB of data.) Tethering for iPhones will be available when Apple releases iPhone OS 4 this summer.

In addition to 3G data, people getting the new plans will have free access to AT&T's 20,000 hot spots. How are iPad users affected? Current iPad owners can keep the $30 unlimited plan or switch to the new $25 2GB plan. For new iPad customers, the $25 DataPro plan will replace the unlimited plan. But unlike iPhone users, iPad owners will continue to pre-pay for their wireless data plan with no contract.

AT&T had been hinting for months that it would adopt tiered pricing for mobile data use as a way to curb use by bandwidth hogs and operate its network more efficiently. The carrier has said 3% of wireless users account for 40% of the data traveling through its network.

AT&T's shift to variable pricing for data could lead to a similar move by rival Verizon Wireless, which has already said it will not offer unlimited pricing for data on its forthcoming 4G network. Wireless industry analysts view a broader switch to tiered pricing as inevitable as carriers handle a growing amount of data traffic