I agree with what has been said here... If he just plans on skipping out on his contract then I would stay away from that fire.. Sprint will blacklist the phone (ESN), his credit will be hit, and it won't be a nice looking hit skipping out on a contract/monthly bill and walking with the phone.
Creditors especially today with the economy and all look at things 10x worse than years ago and a mark like that on his credit will haunt him for years and even once its cleaned up it still takes years to get removed completely from showing up on your credit report (normal is usually 7 years).
Not to mention that mark on his credit, moving to another carrier can bite him in the behind too.. He may get in the door initially at TMobile or some other carrier but they do random credit checks ' inquiries ' just like any creditor on your name and once they see a hit like that from Sprint they can turn and drop him on the spot too... As for those inquiries anyone who has ever ran their credit and received the full credit report will see usually the last few pages of a credit report say Experian or Equafax, etc. will be all the current creditor on your name that have done random inquiries over time to see how your credit is looking and they don't need permission to do so either