If your phone is carrier locked, to use in Europe...as a phone & for data...would be extremely expensive. You'd have to get International Provisioning activated for your account, then pick a plan & pay through the nose. What many folks do is put their phones in Airplane mode, turn WiFi on & use available WiFi for their phone's data needs(although there are not nearly as many free WiFi spots in Europe as there are say in the US). If you want to make calls, you can either purchase a local phone with a pre-paid sim(they are cheap & readily available) or you could still get International Provisioning activated for your account, but turn cellular data off in settings on your phone. That way you could make/receive calls & SMS's but not incur hefty data charges.