I just bought a nextel 7000i from my friend for real cheap. The problem is the scroll and back buttons do not work. Will I be able to go to a Sprint Repair shop and get the two buttons fixed? Do they charge for the repair? Thank you

There will be no charge if you have insurance. As long as that phone is shown active on your account, then you can bring it into their repair center.
The charge ranges from $15-$55 if you don't have their service & repair insurance.