i believe so. also, if the person on ebay was upfront (new phone, box missing UPC code), that's completely fine.

regarding the original post, in theory this is true. buy things with a mileage earning credit card and then send away for rebates. problem is, it's a lot of work for typically small ticket items. yes, your phone had a nice rebate but most rebates are small. plus, keeping track of the rebates is a complete pain. and, if you don't receive a rebate or two, it completely wipes out the value of the miles you did earn since you probably wouldn't have bought the items in the first place. it's just a lot of work....