Its only 16 countries currently and luckily for me France, where we go every year, is one of them. Made up for the fact they added the US a week after i came back!That's what has me red with envy, the fact you can still have all that data even while abroad!!
I'm SIM only so when i switched i initially paid a couple of quid more to go on the rolling monthly deal to see how i got on. Turned out the only place i was in on a regular basis that struggled was at home. I rang 3 to see what they could do about it and in return to switching to a yearly contract they sent me a home signal box which plugs into our broadband and boosts the signal using it. Since moved but still using the box and works a treat.I switched to Three and got a Samsung Galaxy S3 in July 2012 and I had unlimited data since then. I'm still with them now. But planning on switching to EE in March '06 due to their superior coverage in my area, recently moved and can hardly text indoors, calls are a no-no.
They've stopped issuing these now but have a very good app called InTouch which uses wifi to allow you to still get calls and texts to your phone. I dont need it at home but enable it if i'm in hotels or alike and the signal isnt great. You just have to go into the app to say the wifi you are on can be used for the app and it then starts piping the stuff through to you when required. The issue is that the frequency that 3's 3G signal runs on isnt very good at penetrating buildings so if you are in an old building or a deep inside a building then it struggles. Apparently this will get better as their 4G network, free to all 3 users at no additional cost, rolls out further.