AT&T’s new Mobile Share plans will be available Aug. 23, according to a blog post by AT&T CMO David Christopher. Customers will be able to sign up for a Mobile Share plan at any AT&T retail store or by calling AT&T (online sign up will be available soon after launch).

Like Verizon’s Share Everything plans, AT&T has set the maximum number of devices that can be connected to one bucket of data at 10. One of the 10 devices must be a smartphone. Each plan includes tethering and unlimited domestic calls and texts for smartphones and basic or quick messaging phones.

AT&T has built savings into the new plans that give discounts to customers for using more data. The larger the data bucket, the less the customer pays per gigabyte, with an additional reduction of the per-monthly fee for each smartphone added to the shared plan.

For instance, a 1 GB bucket of shared data costs $40 per month, while the connection fees for each additional smartphone on that plan run $45 per month. However, the monthly smartphone connection fee is just $30 per month on a 15 GB shared bucket of data costing $150. Connections for additional devices to the plan include: $30 for a feature phone or quick-messaging device, $20 for LaptopConnect cards and netbooks, and $10 for tablets and gaming devices.

To make it as easier for customers to choose the best plan for them, AT&T has added a Mobile Share Planner tool to its website. The tool offers a way to estimate a customer’s current usage on each device. It automatically calculates total estimated usage and recommends the right Mobile Share plan, from 1 GB to 20 GB. The tool also shows the estimated costs for that plan.