Nope. This isn't about being green and recycling.
I'm referring to the boxes your cellphone units come with. Save them. Including everything inside them, especially if you aren't using them.
See, in cases when you want to trade in your older unit for a new one, units that have boxes fetch a slightly higher price.
And yes, the older your phone is, the lower it's trade-in and resale value becomes, so saving those boxes will count for something.