Couple of things to know before you use a smart phone outside USA. The most significant issue is with data roaming. Data roaming cycles every 15 minutes for emails, etc. This happens regardless of whether you prompt for emails or not. To counter the issue, Apple allows you to turn off Data Roaming prior to leaving us. You can do it directly on your iPhone. Depending on your version the instructions differ a bit. Now if you turn off data roaming, you can still get text and voice calls. Your carrier should have an international plan, but even those are expensive. You can turn off all cellular data so no calls or texts can come in, but that takes away getting the "emergency" calls as well. That is something you have to balance. You can simply turn off data roaming (must do this) and keep cellular data on then turn off the phone until you want to use it.
My first trip abroad with my iPhone took my phone bill from the average $500 per month to over $1,500. I was out of country for 4 days and actually decreased the number of texts/calls. The culprit was data roaming.
Hope this helps