Head over to Apple UK here http://store.apple.com/uk/browse/reuse_and_recycle and find out how much store credit Apple will give you for your old iPhone to help towards than shiny new one.
The service is also live in Germany.
However, if you like eBay you will get more for your money.
Gavin's Gadgets & Photography 
Apparently my son’s old iPhone 4 32gb is worth £1.58! Wow. I’m definitely going to trade it in now.
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That is a bargain lol
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