For an Iphone to be used on Sprint the ESN of the device has to be stored in our data base. If it is not there we cannot activate the phone on our service
I suppose he doesn't have the answer to as if the ESN is loaded on their network, maybe try calling and giving them the details, I thin sprint uses the IMEI which can be find in Settings > General > about... Don't post this code online, you give it to the sprint rep or what ever else he ask, but now you know how to find that information. I think with that he can find it for you.
Don't listen to this Sprint tech, he/she clearly has no idea what they are talking about... The answer to your question, since they decided to NOT answer it, is YES, you can use a Verizon iPhone 4S on Sprints network... How do I know this? Well, because I currently use a Verizon iPhone 4S on Sprints network, it is a bit tricky but it can be done..
The only problem is, Sprint will NOT be able to help you with this, you will have to contact Apple Care Advanced Support Team, you will have to remove the SIM card and have them re-flash the phone, once that is done you are good to go!!
Why am I using a Verizon iPhone 4S on Sprints network? Well, when I first got the iPhone 4S through Sprint, I had it for a few weeks and started having problems with it, it would no longer take a full charge, Sprint could not figure it out (just like everything else) and said I'd need to talk with Apple since I was still under my inital Warranty period, I contacted Apple Care, we looked into getting it fixed but couldn't, at that point Apple decided they would simply replace my phone, they sent out a new iPhone 4S via FedEx Overnight Shipping, I went to the FedEx store in my area and picked it up the next day, called Sprint to activate the phone and it wouldn't work... So I called Apple Care back and spoke with the lady that I had been dealing with, after a little time on the phone with her, I was going through the "About" section under "Settings" and saw that the "Carrier" said "VERIZON", I asked her what that was all about, and she said; they must have sent the wrong phone out, she then had me pull the SIM card, re-flashed the phone and I was good to go, not a problem since then...
So with that said, I'm not sure what "14KNIGHT" is talking about, I think it just comes down to he/she being a typical Sprint employee, not wanting to do their job... Either way, good luck! By the way, I'll be selling my iPhone 4S here soon, when the new iPhone comes out next month, I have TONS of extras with it, it has had a privacy screen protector on since day 1 and a protector on the back glass as well, M-F it stays in a Griffin Survivor case, and I also have 4 additional cases, 3 home chargers, 2 car chargers, 2 stylus pens, 3 foot cable, 6 foot cable, docking station... well, you get the idea, I have a BUNCH of stuff for it if anyone is interested?? By the way, it will work on Verizon OR SPRINT...
BR1LEY You have a rather unique situation You had a pre-exsisting sprint account with an Iphone. Apple mad an error sending you a device. Apple also has the abiltiy to send us the ESN number of the device to load into our system and the abilty to program the device through Itunes. Yes the device had to flashed to show Sprint as the carrier but more importantly the data base of apple ESN numbers had to me updated. So Sprint service would recognize the device.
The esn number has to be loaded into our system. I am not the only one who thinks this http://www.iphonefaq.org/archives/971229
taken from the above website
So does that mean you can buy a CDMA iPhone and use it on Sprint? Unfortunately, no. CDMA providers, such as Verizon and Sprint, are notorious for being unwilling to allow customers to use phones that weren't sold directly by the provider. Though the Verizon iPhone 4 isn't locked, it does contain an ESN (electronic serial number), which you can think of as a mobile phone's fingerprint. In order for a CDMA phone to be activated / used on a CDMA network, the provider must have that device's ESN on their list of approved serial numbers.
In other words, the carriers excercise full control over what phones operate on their networks via the ESN activation requirement