America's top two wireless carriers AT&T and Verizon on Friday announced value added changes to their respective mobile data plans, though Verizon is only offering extra data as a limited time promotion.

AT&T was first to announce data buffs for its Mobile Share Value plan portfolio, with the telecom offering 3GB of shared data for $40 per month and 6GB for $70 per month, up from a 2GB and 4GB, respectively.

As seen in the chart above, AT&T's updated plans only apply to the top-tier plans, leaving out customers paying $20 or $25 per month. The company notes smartphone access charges will remain stable at $25 per month, per line with the Next yearly hardware upgrade program or $40 per month with a two year contract.

In addition, AT&T is extending its Double the Data offer for customers choosing data allotments from 15GB to 50GB. Under the limited time promotion, which runs until Nov. 15, new and existing users can sign up for a 15GB plan and get 30GB of data.

More information is available through the AT&T website.

As for Verizon, the nation's largest carrier announced a limited time promotion for subscribers of its More Everything plan. Like AT&T, Verizon is offering more data to top-tier customers, giving 10GB of data for $80 per month and 15GB for $100 per month.

Verizon's promotion starts on Nov. 1, with no word on an ending date.