Are you a data hog? If so, you might be interested to hear in a new AT&T promotion that's doubling the data offered in its largest plans. The company's current 15, 20, 30, 40, and 50GB Mobile Share Plans will all be doubled to 30, 40, 60, 80, and 100GB for the same price starting tomorrow.

Now that's a ton of mobile data to burn through in a month, but the low prices might be good enough reason to join a large shared data plan with your friends or family to save some money. The new 30GB plan, which is the most interesting of the bunch, costs $130 per month, just $30 more than the carrier's oft-advertised 10GB for $100 plan. That's $4.33 per gigabyte compared to $25 for the 1GB plan. However, the double data is just a temporary promotion — you can only get it if you sign up by October 31st, though you'll be able to keep it for life once you're signed up. It's also worth noting that if you already have one of these plans, you will need to contact AT&T to get the double data upgrade.

If you're not familiar with AT&T's Mobile Share plans, they offer one large bucket of shared data among users on a single account, and they include unlimited talk and text. You have to pay extra for each device you add, however: $40 per month for every on-contract smartphone ($15 if you upgrade with Next or buy a phone off contract), and $10 per month for each tablet. The promotional pricing brings AT&T closer to third- and fourth-place carriers Sprint and T-Mobile, both of which offer unlimited data plans for similar prices as the new 30GB Mobile Share plan.