The poster above is correct. Sprint does not report to credit bureaus. However, if your account is sent to a collections service, then that will be noted on your credit history. The good news is that you can usually make arrangements to have that removed once your account is settled. Contrast that with being late on a credit reporting account...they almost never remove the ding on your credit history.
If you are looking to build credit, I would suggest a credit card. Do not apply to more than 3 as each credit pull will affect your credit. There are websites that compare cards offered by different companies for different classes of credit. Look for ones that say "building credit". They usually have an annual fee, but once you get your score up, you can ask for it to be waived or get a different card. If you are a student, apply for a student credit card. These have a lower FICO score requirements. Lastly, you can always sign up for a secured credit card. Just watch out for those with tons of unnecessary fees. Good luck.