Is there a charge for Sprint to change my phone to one I get on ebay?

I'm looking into getting an Instinct on ebay for Christmas, but I was wondering if there will be a charge to switch from using my Razr phone when I get the new one.
We've had our contract with Sprint for about six months and our phones just as long. There's really nothing wrong with my phone, I just want something better than the Razr
I don't need to transfer the numbers over; I can do that myself. I'm not some old technologically challenged person...
I'm not dissing old people, I'm just saying I know more older people who don't know much or anything about computers, like my grandmother, who doesn't know how to use her computer for anything but playing Hoyle Casino or Card games on it.