Unlock BB Tour from VZW to use with Sprint?

First I would like to say sorry if there is already a thread about this, I did search and was unable to find info here or anywhere else that I looked.

Now down to business....

My GF has a BB tour with Verizon her bill is currently running about 125 a monthy!!! If we can unlock her phone for use with sprint then we can save about $75 a month. Is there anyway to unlock her phone? what about installing a sprint rom? Any help you can give me would be greatly appreciated!

-Noble