If you are on AT&T's Mobile Share Value plan, here's some good news: starting today, the carrier is offering 15GB of data for the current price of 10GB -- $100 per month. This is a limited time promotion, although the company didn't specify when it would expire.

The offer is available to both new and existing AT&T customers and includes domestic unlimited talk and text. However, there is an additional smartphone access charge of $15 per month per line for "a smartphone purchased on AT&T Next, or at full price, or when a customer brings their own smartphone, or has no term commitment". Those who are on a 2-year wireless agreement will have to pay $40 per month per line.

The promotion comes just a couple of weeks after the nation's No. 2 carrier boosted data by 50 percent in its $40 and $70 plans, offering 3GB data instead of 2GB, and 6GB instead of 4GB, respectively. That offer also includes domestic unlimited talk and text, is available to both new and existing customers, and has no expiration date.

Prior to that, AT&T also doubled the amount of data users get with its 15, 20, 30, 40, and 50GB plans at no additional charge. The promotion applied to both new and existing customers, but was valid until October 31, although it was later extended to the 15th of this month.