This is directly from AT&T's website:
"About AT&T Mobile Share plans
AT&T Mobile Share plans provide both individuals and groups with value, flexibility, and simplicity. We're pleased to offer two types of Mobile Share plans, Mobile Share Value with Unlimited Talk & Text****, and if you don't need voice services choose Mobile Share - Data.
If you have multiple devices on your account, you'll have the flexibility to share data ranging from 300MB to 50GB with up 10 devices per Mobile Share group. If you only have one device on your account, use all the data yourself. If you need to accommodate more than 10 devices, you can add more than one Mobile Share group to your account. Mobile Hotspot is also included at no additional cost, which allows you to use compatible devices as Wi-Fi hotspots."