AT&T was one of the first carriers in the US to institute data caps on smartphones, and it has recently taken some heat for its treatment of grandfathered unlimited data customers. Maybe looking to smooth things over a bit and earn some good will, AT&T is boosting the caps on two of its Mobile Share Value plans.
If you're on the 2GB ($40) or 4GB ($70) data tier, you are getting a bump to 3GB or 6GB with no increase in cost. This is just the data charge, of course. You still have to pay the line access fee on top of data. That said, there don't appear to be any additional strings attached. You get more data and that's it.
In addition to the cap boost, AT&T is extending its double data promotion for the high-priced plans of 15-50GB. These are the ones you'd get with a family of heavy data users. Each of these plans gets double the data if you sign up before November 15th.