I don't have the address to SPRINT but I do have a good number for them: 188-456-6070. The person I delat with name was John. You can most likely call them and ask for a address or fax number for them. Good luck!
The contact number for Sprint PCS is 1-888-211-4727. It's not specefically to the collections department, but the rep can tranfer you over to that department. Also the general Sprint PCS address from my bill is: PO Box 219554
Kansas City, MO 64121-9554. Not the address for colletions specefically, but an address to Sprint.