Apple's trade-in program would always reject iPhones that had their liquid contact indicator tripped. According to Apple retail employees this will no longer be the case. This week Apple will take in iPhones that have their liquid damage indicator tripped, but not iPhones with serious water damage. They will check for evidence of corrosion or liquid build-up.
This could allow Apple to push the sales of more iPhones. The Reuse and Recycle program will allow you to get credit to spend at Apple stores or their website. This will be applied to the US market and the UK starting this week.