How to trade in my smartphone for the iPhone 4s?

Since the iPhone 5 came out I want to get the iPhone 4s because it has decreased in value. Right now I have the Samsung Galaxy s 2. My contract is not up to get a new phone though. I was wondering how I could push up my contract, and maybe sell my current phone to att. What can I do to get the iphone 4s for the contract price ($100) I don't know what to do. Please help, thanks~

Sell your Samsung & put those money towards new iPhone.
You can get an idea on how much S II sells for and even sell it here: http://www.gadgetsalvation.com

Multiple reports that Apple will hold a special event to unveil its next iPhone have resulted in a noticeable boost in people trading in their old devices, eBay said today.

http://news.cnet.com/8301-13579_3-57485862-37/iphone-5-event-rumors-pump-ebay-smartphone-trade-ins/

You could use a service like Nextworth to get cash for your phone. Then you can put the cash towards a nice iPhone 4s. Receive a quote at Nextworth.com.