I've yet to see such happen in any country. There's always some network that won't work. And beyond that you wrote FULLY. I have phones that for some odd reason at some locations can't get a data connection.
All I can take away from this is there is no perfect phone or carrier.
Will a Samsung Galaxy Duos work FULLY in the uk on all networks? Including the pro versions with the keypads. If so where would you advise to buy one online? Would suit me as I am always swapping phones and its the only phone I have found to do this. thanks