All AT&T Mobile Share plans give you unlimited calling, texting (domestic) and let you tether a smart phone to another device. This is called the hotspot feature. Most newer (last 2 years) smartphones can do this. You pick the amount of data you want. Their best deal is a price match to T-Mobile: if you are out of contract you get the above with 10GB with two smartphones sharing that for $130/mo. Each add'l phone is $15. 10 max allowed.
We were paying the same I think for 4GB before they brought this plan out earlier this year. I could have my tablet activated as it is cellular ready however I don't need to with the Hotspot feature of my phone.
It really pays to call every three months or so no matter who your carrier is to be sure they don't have a better deal. Very competitive industry and plans change.