[elephant007]

So let me see if I understand you

you currently have Sprint as your cell phone provider
you purchased a phone from someone and want to have it activated to your account
Sprint wants you to sign a 2 year contract in order to active this phone to your account
they won't activate your phone unless you do sign a 2 year contract

If that is the case, login to your online account and active your phone yourself
If you're swapping phones, you should be able to do this
If you're adding an additional line to your account, yes they will ask you to sign a 1 or 2 year contract if you're switching plans.