It's a right sod working this lot out, for sure. For years I had to pay three pounds a day to take my call plan into Europe, but now I can use my plan as though I'm at home. Good old EU.

Here's the rub. If you have a broadband contract, or can log into your son's/daughter's/friend's/any other sucker's wifi, all will be gloriously and limitlessly free. It's only when you use a 3G or 4G connection that you'll be using up your data allowance. Most activities, such as googling things or checking/sending emails, are very light on data usage. Stuff such as watching TV, downloading films or streaming music are heavy on data, even FaceTime, but, if you have several gigs and don't do stuff like that very often, you'll be fine. If you have a smartphone, and you're using it on 3G or 4G, you are using data. If you tether your tablet or laptop to your phone whilst on 3G or 4G, you are using data faster than if you were just on your phone because you will be constantly downloading large web pages wot you don't download just on your phone. If you are in environment in which you can connect to wifi, even if it's not your wifi (in which case just get the password for that wifi network) there's no point tethering your laptop to your phone, as you'll be able to connect your laptop to the wifi directly anyway. As I said before, before you resort to tethering, just check that your ISP doesn't charge extra for it first.