What happens to the IPhone when you travel?

So I was planning on going to Mexico and IIm from the USA and I was wondering can the iPhone still work normal like if I was still in the USA? Or is there a process to be followed?

What you mean

You need to go to the ATT site and read about international data and calling. Not sure about Mexico - but we will be in Budapest for a few weeks, and bought a $30-each international plan form ATT just as a precaution - you only get 120 MG of data (each of 2 phones) and the *privilege* of then paying a buck a minute to call home. The heck with that - we will call using Skype - free to our family that has it, 2.3 cents a minute to call to landlines and other cellphones. I have some WiFinder apps, and will just plan accordingly, and use hotspots and free Wi-Fi where we can. We're NOT there to do business and live on our phones - most days, our few people to contact at home will survive with a text (free). So as I said - Mexico will be different than Europe, so do NOT jump in any pay ATT for something you will not need - or need much - especially if you are going to be places with no signal anyway. If I have time, I will check this out for you.

Added - go read it for yourself for more info - but it seems that if you get that Passport plan ($30 god for one month) you get the data I said; texting is free; and you get to pay a buck a minute to talk You can get 3 different CALLING plans (no data?) and pay 38 or 30 cents a minute - or you can just use SKYPE like I said. Pay as you go calling is a buck a minute from Mexico to anywhere, too.

Imessage and facetime is always free even internationally as you can use over Wi-Fi. Phone calls you need an intl plan.

You'll have to talk to your carrier about International Roaming since you're willing to use the phone fully in Mexico but charges will apply although it will be cheaper in Mexico and Canada than rest of the world.

It depends on whether or not your carrier supports roaming while abroad.