Admittedly a noob question, but I couldn't find it in ATT's documentation or on a google/MR forums search. I have one of the new ATT mobile share plans, I have 2 iphone 4s on the plan and pay an extra $10 for my ipad to share data. I never knew about the mobile hotspot feature and to my understanding it means I can share my 4g data from my iphone to any wifi enabled device. Enabling this, is this free? Do I have to register or pay for the device that is piggybacking? One reason I ask is because I'm wondering if it's worth paying the $10 for my ipad if I carry my iphone with me all the time anyway and can just mobile hotspot, another reason is I would also like to mobile hotspot a laptop to my iphone.