Companies could boost sales by offering trade-ins

I think that some technology hardware companies like HP or Apple would be able to boost their sales if they offered trade-in opportunita : weies for their products. while that they would have to dispose of the thing being traded-in just think of the new product sales they would achieve by giving a discount just for being a loyal customer.

Just think at how many people are in the same boat as me-they currently own an iPod but want the iPod Touch. Giving a $100 discount would mean I would spend $200 on the new device. Better still they then would be able to cannibalize the trade-ins for spare parts or use them as test equipment or give them away.