Re-flashing iPhone 5 firmware

Every iPhone since the 4S has a record in Apple's database. While the database is managed by Apple, the data about a phone in Apple's database is "owned" by the carrier, not by Apple. So Apple cannot legally edit the record without authorization from the carrier. Prior to the 4S only GSM phone's lock status were recorded in Apple's database; CDMA phones were not. The database record for your phone contains information about the lock status of the GSM side of the phone. It can be unlocked, regionally unlocked, or locked to a carrier. If it is locked to a carrier or regionally unlocked (which means locked to a carrier, but unlocked by that carrier for certain geographies, such as "not in the US") then the GSM radio is considered locked. A CDMA carrier can choose to support only the CDMA side of a phone, but none do except for the iPhone 4/CDMA and earlier. As CDMA is being phased out, this is not a surprise. As the phone is apparently recorded as locked to Sprint in Apple's database you can only use the GSM/LTE radios with Sprint, not with Verizon. Verizon will not activate a phone that supports GSM/LTE for CDMA only; they will only activate a phone that supports GSM/LTE and is unlocked for it.

The most recent information we have heard is that if you have an unlocked (meaning GSM/LTE unlocked) iPhone 6, 6+, 6S or 6S+ Verizon will allow you to register it on their network. This "BYOD" (Bring Your Own Device) is a relatively new policy for Verizon. Again, the last we heard is that these are the only phones that Verizon will do this for. The source for this information is a Verizon support rep who is also active in Apple Support Communities. If you get the phone unlocked by Sprint (if you can) you can use it on AT&T or T-Mobile.

As has already been mentioned, iPhones are not unlocked with a code. If a carrier agrees to unlock a phone they send an electronic request to Apple to change the lock status in the database, and about a day later you can Restore iOS on the phone to unlock it. The Restore process re-activates the phone by querying Apple's database, and, if the phone has been properly unlocked, iTunes will display a message saying that the phone is unlocked.

mmbridges wrote:

I think you have already stated that overiding the database entries would be a violation of their contracts withe carriers. But does flashing to the factory state firmware, if technically possible, also violate their contract with the carriers?

The lock status of an iPhone is not stored on the phone. It is stored in a database. When you activate the phone it connects to the database and reads the lock status, then enforces it. There is nothing to flash on the phone. The only software on the phone is a boot loader and the iOS operating system. The boot loader is in ROM (not programmable; old-fashioned ROM, not EEPROM, or flash memory, but permanent ROM). Everything else is loaded when you install or restore iOS, including the modem firmware (which is carrier-specific), the carrier settings, the operating system, and the default applications.

Could this be the process they won't guide you to?

There is no flash backwards. Just a full re-activation I guess.

How to unlock your iPhone for use with another carrier - Apple Support

Why would you want the store to do that as opposed to using the restore function of iTunes?

File a complaint with the FCC on their website fcc.gov. Send a copy of it to the CEO of Sprint.

The only thing that can be changed in regards to the phone service is the nanoSIM from a cell provider. There is no EPROM to flash or that is flashable in the iPhone.