The price-war among the U.S. mobile phone carriers isn't entirely new, but the continued competition is surely benefiting the consumers. As all major carriers fight to gain supremacy in the market, AT&T and Verizon have stepped up their efforts with revised monthly data plans. In what is seen as a reaction to Sprint's new double-data offer last month, the two biggest carriers in the U.S. have almost doubled their monthly data limit at no extra cost to attract more subscribers.

In a press release, AT&T announced the revised Mobile Share Value plan to give a better worth for the $40 and $70 plans. The base plans offering 300MB and 1GB for $20 and $25, respectively, remain unchanged. But new and existing customers opting for the revised $40-a-month plan will now get 3GB data instead of a 2GB bucket. Similarly, those who choose the $70 a month plan will get 6GB, up from 4GB. The $130-a-month plan offers double the data at 30GB.

In addition to the new offer, AT&T also extended its limited time Double the Data offer on its Mobile Share Value plans that gives twice the data for the same price. The offer, which was originally announced in September and valid till Oct. 31, is now valid for those who sign up before Nov. 15.

Verizon also stepped into the competition with its new offer of an additional $150 credit for new customers porting in from a rival carrier. As for Verizon's More Everything plans, higher-tier plans get a data boost starting Nov 1. According to Verizon's official blog announcing the new change, the $80- a-month plan gets 10GB data instead of 6GB and the $100-a-month plan gets 15GB, up from 10GB. The change also applies to the $130- and $150-a-month plans, which now offer 30GB and 40GB, respectively.

Despite the changes, Sprint continues to offer the best plan that gives 20GB for $100, two times greater than T-Mobile's data allotment and by far the cheapest option among all the four carriers.