Okay, I feel the need to step in and play devils advocate here... What you have in your possession is a blacklisted phone that was reported lost to Asurion/Sprint. You are the customer whom has filed said claim and received a replacement phone to replace this missing property. While even I could advocate keeping the device around for testing purposes, its clear that the services are still being routed to the device. So lets play out a scenario...
Sprint deactivates the voice services from the line, leaving only a Mobile IP attached to the device therefore allowing internet to remain on. IP addresses are traceable to a great extent by the ISP in charge of the address. Your device also happens to be equipped with a GPS chip tied into the aGPS functionalities of the device. Put two and two together. While it may not seem plausible that they would do such a thing, they will eventually notice that there is bandwidth going where its not supposed to be going - even in minor amounts. Would you want to be the one streaming porn to your notebook when an investigator walks up asking you for the device in question?
It may seem like chicken feed to you in that situation - but Sprint will see two separate (maybe more?) lawsuits right away - 1) Insurance Fraud: you agree to return lost/stolen devices if you recover them after the insurance claim - its in the TOS, and 2) Theft of services: you using internet on a device that is supposed to be deactivated is really no different than running your own cable TV line from an unlocked tap - which especially lately has been getting easier for the providers to discover.
All I am saying is that you are carrying an easily locatable device and using services you arent paying for. Its really up to you whether its worth the risks associated or not. I just figured I would give it to you from the other side of the coin my friend. Good luck with it either way!
