T-Mobile is once again having an impact on the rest of the wireless industry. After announcing its Data Stash program late month, AT&T is now following suit and will allow select customers to carry over unused data to the next month.

Later this month, AT&T will offer rollover data to all new and existing customers that are signed up for one of the company’s Mobile Share Value plans. At present, that consists of more than 50 million customers so we’re talking about a change that will impact a large portion of AT&T’s subscriber base.

It’s worth pointing out, however, that AT&T’s offer isn’t quite as attractive as T-Mobile’s plan. Under John Legere and company, rollover data expires after 12 months. With AT&T, any unused data is only available to use in the subsequent month and only after a customers has exhausted their standard monthly allotment of data.

For example, if you have four lines with a 15GB Mobile Share Value plan and only use 10GB in a given month, the remaining 5GB will carry over to the next month so you’d then have 20GB. If you again only used 10GB the following month, you’d still only carry over 5GB of the original 15GB allotment to the next month.

The feature will automatically be enabled on all Mobile Share Value plans starting January 25 at no additional cost. Customers will be able to keep track of their rollover data on AT&T’s website or through its MyAT&T mobile app.