Even though Verizon has promised an OTA update sometime in the (undisclosed) future to bring true global roaming capabilities to their flagship Samsung Galaxy S III, waiting for them (or any carrier for that matter) to make good on promises is often a long, long waiting game full of frustration and broken promises. Because of this, we often suggest users take matters into their own hands – in this case, enabling global roaming without Verizon’s help.
Once again it is XDA providing the goods, with these two posts detailing the steps necessary to unshackle that VZW branded Galaxy S III and turn it into a proper globe trotter. That said, the process is quite involved, more-so than your typical root/ROM flashing ordeal. As always, be careful. A bricked phone is useless. Hopefully Verizon finally follows up their original promise with an OTA update that unlocks the aforementioned feature sooner rather than later.