Another Amazon consideration for European roaming service are the "3" UK network sim cards. They can be had with 12 Gb of data and voice service good for 30 days for around $20-$25 usually. It gives you a European number also which can be handy for calling hotels, cabs, etc. locally. The data service will permit the IMS procedure to give free USA calling also. You can set it up for testing prior to departure from the US, so no hunting for shops, language or exchange issues.