Use my iPhone in Europe

The simplest thing.....by far.....is to check with your current carrier to see if they have an International Plan option that you can add to your current plan.

That way, your phone will automatically roam and pick up a carrier in whatever country you arrive in and automatically switch to another carrier in another country as you travel.

The simplest thing to do would be to contact your carrier and ask what their daily roaming fees would be.