Does it have to be an iPhone or could it be any sprint phone if yes how
it can be any phone (I personally flash phones as a side job) here's a quick guide.
Download a Verizon/page plus .prl (preferred roaming list) and flash it with with either the cracked version of CDMA workshop 2.7 or dfs tools demo edition.
For ota programming make sure to change the MSL/spc to 000000 and dial *228 or u will have to manually program the phone to get calling and texting working
Data and MMS is different for almost each phone so I'm not going to write a whole tutorial here but if anyone is afraid to play around I do most flashes for $30 and will help anyone for free if I'm not to busy so either email me or pm me