So, not addressing the fact that AT&T's "Shared Data" plans are in fact the exact opposite of what they are called (I guess a tradition from the "Unlimited Data" plans that just won't die), I wanted to try and look at the new plans and actually see what the cost comparison is to current plans.
I think the best way to think about these new plans is just a new pricing scheme, rather than a new service. I worked out the numbers in the easiest way I could think to display them.
Savings with the new "Shared Data" Plans
Generally, if you have a family plan, with all smartphones, and unlimited texting, the new "Shared Data" plans will actually save you money. Below is a breakdown of how much money you would save by switching over to the new "Shared Data" plan.
The savings are based on if you choose the "Shared Data" pool that is closest to what you get with the current plans (i.e. 3 phones get a total of 9GB currently, so it is closest to the 10GB shared plan). Obviously, if you don't use all the 3GB of data per phone from the current plans, then you could save more by getting a smaller bucket of shared data. Likewise in the opposite direction, if you need more data, you won't save as much.
Below are all the "Current Plan" rates, based on plans that have the $30/month unlimited family texting, and each phone is a smartphone with an individual 3GB of data at $30/month. This table shows the breakdown of the Unlimited voice, 2100 mins, 1400 mins, and 700 mins family plans that are currently available. The right hand side shows you the total GB of data you are getting, as each phone adds 3GB of data for that phone.
"Shared Data" Plans
Below are the costs of the new "Shared Data" plans that AT&T released.
These numbers are based on if every phone is a smartphone, and keep in mind that these plans include unlimited voice and texting for each line.
Breakdown of Current to Shared Plans
Here is the breakdown of each of the 4 Current family plans (Unlimited voice, 2100 mins, 1400 mins, 700 mins) vs. the new Shared Data plans. The Current plans are taken from above, meaning that they include unlimited texting, and each phone as a smartphone, with the $30/month for 3GB of data.
Outlined Boxes - The closest plans comparing total GB of data from the Current Plan, to the shared bucket of data in the Shared Plan (i.e. 3 phones get a total of 9GB currently, so it is closes to the 10GB shared plan)
Green Boxes - Indicate that those Shared Data plans are cheaper than the Current plans
Red Boxes - Indicate that those Shared Data plans are more expensive than the Current Plans
Difference from Closest - This column is what made the "Savings" section above. This is the difference between the cost of the Current plan, and the Outlined Box (closest equivalent to Current)
These charts show that in pretty much all cases, the Shared Data plans are cheaper than the closest equivalent Current plans. And in most cases, you can in fact get a larger bucket of shared data, and still be cheaper than your equivalent Current plan.
Again, just keep in mind, these numbers are assuming that all phones are smartphones, and Current plans have the $30/month unlimited family texting.