AT&T announced Wednesday that it would start offering metered data plans for mobile device users rather than a $30 all-you-can-use monthly plan. For people who use less than 200 megabytes of data a month, the price of the new plan is effectively cut in half. The latest announcement could signal the beginning of a new arms race between mobile phone carriers. In the past, carriers tried to woo customers by offering mobile packages that were gauged by the number of voice minutes available each month.NYT: AT&T Eliminates the Unlimited Data Plan