answer:I don’t know a lot of information on this, but I’ll answer what I can. You can purchase sim cards all over the place. Each sim has a unique phone number. To add more minutes to a phone you purchase credit. You can buy this phone credit in the majority of newsagents and shops. You can also phone (depending on your network) and top up the credit using a bank account. Depending on the network provider of the sim (Vodafone, 02, Orange etc.) you can use the sim all over Europe. But there will be Roaming charges, though each network probably has there own offers or plans you can sign up to so that you get the best value for your money. I would look up network providers in the country that he is first visiting so that he can know what pay plans they have etc. so he knows which sim he is going to choose. Though it will probably end up cheaper if he buys 3 sim cards, one for each country. As they only cost ~€20. It might save him having to sign up for Roaming plans etc. Though that would mean 3 different numbers for the 3 different countries. Hope that helps. Anyone else please feel free to correct me if I’m wrong.