works right out of the box, no modding/ hacking required after installing ICS. Simply installing ICS unlocks the GSM band. There's an option to manually switch between CDMA and GSM modes in settings > more > Mobile networks > Preferred network mode, but mine was on global and connected right away after boot.
Only extra step is to manually add APN
I have been reading through the forums and so far no one in the states could get GSM working. I suspect Verizon blacklisted the gsm networks.
Check this thread for ICS upgrading instructions
I had my oem motorola recovery disabled after updating (probably botched up a step) so YMMV