How to have a Verizon Iphone converted to Sprint service? - 1

Does the phone HAVE to be flashed? And if so, how/where can it be flashed

Yeah, and you would need a flashing tool and the rom from that exact phone from the other carrier

I'm not 100% sure this can be done. Verizon and sprint use different cellular technologies. Verizon used CDMA or Code Division Multiple Access, and sprint uses TDMA or (I think it stands for) Time Division Multiple Access. I can't be sure if this is a hardware or firmware change.

No. You can't covert an Verizon iPhone to Sprint. If you want to switch, sell your current phone on Ebay.