I made the mistake of upgrading my phone plan about 3 months ago to a Samsung Infuse and i hate it. now that the iphone 4s has come out i want to buy one but i dont want to pay full retail, i found someone selling a unopened 4s but i am just unsure if i should buy it with all the problems with the activation and DOA units. if i bought a phone off of someone else would i be able to get a replacement or help if it did not function?