Default [Q] Is there a reason to not upgrade and get a free phone?

I apologize if this isn't the appropriate place to ask this question.
Long story short, I own phone "A" on contract with ATT. My dad got me international phone "B", which I replaced phone "A" on the same contract, same carrier. In June I can upgrade my phone for another 2 years contract, but I still want to use phone "B" (it's the awesome note 3) while paying 0 dollar for the discounted phone "C" to keep it like an ipod touch; phone "C" is a crappy but new contract phone.

Is this a possible scenario?
because I could either keep paying 60 bucks a month for phone "B" for 2 years
OR I could get phone "C" for free, pay the usual 60 bucks a month and still go on for 2 years using my old phone "B"
Thank you!