How much is the T-mobile Samsung :) T359?

I already have a phone and I got it a few months ago, but I don't like it anymore. On the T-mobile website, it said that it was $20 for the Even More Plan. (I am on a family plan). How much would it be if I got that phone? Would it still be $20 or would it be more because I already have a phone?
 
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