Can I change carriers by simply flashing roms?

[ApeXz]

I have a Sprint Touch Pro, but would like to flash it to metro pcs. I am a bit of a newbie to all of this. I was told I could flash my phone to metro using their metroflash service, but no store in my town is currently doing it. Would I be able to flash it over myself, simply by flashing to a metro pcs rom? Would my phone be able to go onto their service by doing this? Sorry if its a stupid question, just trying to figure out how I can get my phone on their service for free.