Service Update Codes
These are the ## codes for activating or updating the service on your Sprint phone. You will usually have to run these after activating a used device as it will not automatically look for service when you turn it on. I would always start by Hard Resetting any used phone that you may have to activate again but just in case you do not want to erase everything off that phone you can force the activation with the following codes -
##update# (##873283#) Which updates the service to the phone. This can also help with weak connection and kicking on the internet when it is not working.
##clear# (##25327#) This one actually erases the previous programing and forces the phone to reprogram the phone. I have seen cases where Sprint phones will work after running the ##update# but with some quirks, for instance I switched phones with one of my employees and anytime he called me it came up as my Voicemail. I know weird, well ##clear# will fix any of those little quirks that come from using someones old phone.
Of course once again if you don't care about the info on the phone just hard reset it. The phone will go through the activation process like a new device and there should be no need for these codes. Also on any iPhone device you can just go to Settings->General->Reset->Reset Network Settings. This will only force the programming and will not delete anything from your phone.