Not all phones have sim cards but those that do sometimes they get damaged and slow down the performance of a phone. They usually don't get damaged as much as just get old. I had a phone that was not working up to speed, bad service, dropped calls and slow as hell. When taking it In to be looked at it was suggested to purchase a new card witch they transferred all my info from my old card to the new card and was up an running like new. They just get old like battery chargers. By the way T-mobile charged me 50 bucks for a new card. Google for more info, there's a lot of good info about the good of having extra or new cards.