I just got a 4G android Motorolla Atrix 2 cell phone. The salesperson at radio shack took my sims card out of the box and laid it to the side. He then put my old 3G card in my phone. I asked him wasn't I suppose to get the new card. He insisted that the 3G card would work fine and kept my card provided in my phone box from ATT. Now was he telling me the truth? Or will the 3G card affect the performance of my phone?