Have a look at their coverage map and you can see in the dark blue what 3G coverage you might have got:
http://www.three.co.uk/Support/Coverage
In rural Scotland you are wiser not to expect much ... hence all the comments from those of us that live and frequent the areas outside the Central Belt
I live with an O2 mast at the edge of the farm, but it does not push out data, so although I get an excellent phone signal for voice I get only GPRS speed data.
If you want to see how much 4G coverage there is in the whole country just click on the pink 4G bit on the left then scan around the map for a game of spot the "pink" coverage.
