Have you looked into MVNOs? There are plenty at half the cost of AT&T or Tmo right now.The age of the phone is not what's important but whether there are custom roms available, which there are, KitKat being just one of many. Not to mention there is still active development going on for the S3. As far as T-M or AT&T their plans are just to expensive when you add data and text messaging to the plan ($70 to $80 or more as opposed to $35 a month for everything).