MacRumors on AT&T’s plans for shared data plans:
Shared “family plans” for voice minutes have been available for quite some time, and a similar mechanism for sharing data seems to be a natural evolution. But aside from sharing data among family members, even individuals could see a benefit from the plans, which would allow them to subscribe to a single monthly data allotment that could be used with their iPhone, iPad, and perhaps even a USB modem or mobile hotspot device.
Being able to share a single data plan between devices would make me much more likely to buy a 4G-equipped iPad next time around.