My son will be studying abroad in Hungary for the next four months. His plan is to communicate with us in the U.S. through Viber or Facetime, but wants an international SIM card for texting and local calls or for emergencies in non-wifi areas. He will travel to some extent on the weekends to Austria, Germany, and Italy. Is there a SIM card you would recommend so that he only needs one card rather than need to buy a new one in every country he visits? Would he be able to make calls to the U.S. for those times he doesn't have wifi? Thanks for your suggestions!