I currently live in Vancouver Canada but will be moving back to the states tomorrow.

Currently I am using a Motorola Atrix on Rogers. I have it unlocked and use it on At&t when I am in the states and I found out that it also works on O2 while in London.

Now I'd like to upgrade to the Samsung Galaxy S3 and I keep reading that it's a quad band and that it should theoretically work on both Verizon and AT&T. After returning to the states I'd like to reactivate my Verizon account with a S3 but want to have the ability to be able to use it on O2 in London as I'll be moving there in about a year and will be traveling there for work quite a bit over the next year.

I was just wondering if someone could shed some light on the ability to be able to use the S3 with multiple carriers without having to worry about which carrier to purchase the phone from.

Thanks for your help in advance.