I think thats so GREED and ripoff when people buy iphone 4 for $399 with 2 years contract and then they sell it for $800, when sold, people keep the simcard in old phone. Is there any way cell phone companies can stop them by something that simcard wont work with other phone if people try sell new phone? Or when buyer got iphone the simcard will not work this because its not their name and serial number. The way people cant be GREED and RIPOFF by sell over-price.