If I get an Atrix (as I plan to do in about 30 minutes) I have heard about this "new SIM" for the $g phones. Problem is this, I plan on keeping my Moto Defy that I have been using on ATT for a few weeks for those times I want a tougher phone (swimming, working on the car, camping, whatnot) ...Will the new SIM work on an old phone? (non 4G?)