How do you know if you have the latest OTA in your phone and why is the purpose of the GSM update to be able to use the phone in europe?
The global phone ruu zip file was leaked by Android police website on Aug 15 2012.
[Exclusive Download] Full RUU Build 4.03.605.2 For The HTC Rezound
It has not been released OTA by Verizon.
The version is 4.03.605.2
You can check in system settings, about phone, software
The current, official, Verizon supported OTA version is 3.14.605.12, you can check it by going to Settings-About Phone-Software Information, the Software number should show "3.14.605.12 710RD" and that is the current "official" Verizon firmware, but it does not support any global mode options.
Like HowardZ said above, the global mode leak is out there, it is an semi-official, digitally signed, HTC firmware but not authorized/approved/supported by Verizon, my understanding is that you can just pop in a foreign SIM then change to Global Mode in settings, reboot, and it's good to go. Other than that there are handful of fixes that most people would never notice over the official version. Going to this version is pretty easy, but realize it will likely make it so that you can't receive further OTA updates and would have to manually the RUU again once it comes out. Note that flashing an RUU will factory default your device!