Are you and your family so-called "data hounds," who need much, much more mobile data per month than the average user? Then for God's sake, avoid the limited plans on AT&T and Verizon, and go for T-Mobile or Sprint instead. But if those carriers aren't an option (say, because you occasionally like to stray beyond the limits of major metropolitan areas), then you'll definitely want to check out AT&T's latest data promotion.
If you sign up for a new AT&T Mobile Share Value family plan starting today, you get double the data for the same price, starting with the $130 tier. So, for $130 split between 2-10 lines, you get 30GB of data instead of 15GB. The upgraded tiers are now $150 for 40GB, $225 for 60GB, $300 for 80GB, and $375 for 100GB. These prices do not include the $15 per line smartphone charge ($40 per line for those who go with a more traditional 2-year plan), and customers with single lines or the 10GB Mobile Share Value plan are not eligible for the double data promotion. So, the lowest anyone could possibly pay in this situation is $160 for two lines with unlimited calls and texts, and 30GB of data.
Putting aside for the moment that most customers don't really need that much data, this is clearly meant to attract people who might be tempted by the aforesaid unlimited plans on other carriers. And at face value, it's not bad - if you look at it as an $80/month, 15GB plan (that has to include at least two lines), it's reasonably competitive with T-Mobile ($80/month for unlimited LTE). Sprint still has them beat with a $60 unlimited plan, but frankly, a lot of customers would probably cough up the extra charge and deal with a 15GB limit for better coverage and the ability to use any GSM phone.
You'll need at least two users to make the AT&T plan effective at that price, and already have compatible phones (or use the AT&T Next full-price financing) to avoid the $25 per line monthly charge. The promotion lasts from today, September 28th, to October 31st. The extra data lasts the length of your contract. New customers or those who add an extra line also get a free $100 credit off their bill.