welcome to the forums!!!!!!!!!!!
i have not heard of flashing over to verizon completely but you can roam over to verizon's tower. now keep in mind that if you over do it you can and most likely will get the boot from sprint.

here is the thread about it:
[6/16]*techknowfile's* - Hack the HTC EVO - 3G w/o Sprint EVDO coverage!

and here is a thread from a member (or two) getting the boot because of this:
http://androidforums.com/evo-4g-all-things-root/337563-here-goes-nothing-trying-get-vzw.html

edit: but you do need to be rooted.