A couple of things to think about before deciding to do this.
I know of a few that flashed sprint to Verizon.
If your lucky, you'll receive sprints 3g data which is already pretty horrible. Worst case you'll be limited to edge, enough said lol. MMS pretty much won't work from what I've heard.
I'm not sure about sprint, but the sprint that went to Verizon was restricted to prepaid.
Honestly have no clue if sprint offers prepaid. Sadly I'm with sprint lol
You would need at least a 3g donor phone to start the process and have knowledge with qpst (I think that's what it is) and possibly cdma workshop.
But that's all I can touch on that subject.