As already mentioned, telestial is very expensive and their sim cards rates are very high. The site mentioned above has reviews on several international cards. Of all the international sim cards I have used, United Mobile's UM+ is the most consistent and reliable. The rest keep changing or have totally ceased to function. Obviously, for any extended stay in one country, a local sim is your best bet. Even if you you will be in any EU countries, you can just roam with the local sim from your first country, since the rates are not too bad these days.