Fool-proof way to prevent international fees/roaming charges?

I have been burned in the past with my kid's phone bills while on spring break in France. If I give them a "burner" phone with a French carrier's SIM card (purchased in France after they arrive) AND insist that they take their AT&T SIM cards out of their "real" smartphones will I avoid all AT&T charges?

I have no idea but when my kid was in France we insisted she communicate through wi-fi (facebook, gmail chat etc) There really is no reason for phone use, in my opinion.

you can purchase the sim here in the US and do the replacement prior to leaving. You will also have the French number then as well. I have used this company in the past, most recently 2012, with good results. http://www.telestial.com
They have data and phone only plans.

@Boomie, yes, my plan is to get a mega-mega data plan not voice. They want to be able to get data even when they are away from wi-fi hotspots. The one thing they have shown a weakness for when travelling alone is Google maps. They depend on them even if I give them a paper map
I realize they do not need our home "burner" phone they can just pop the new SIM cards in their iPhones. That used to not be the case. I think their iPhone 5's have the correct bands to use internationally.

AT&T customer service will tell you if the phones are travel-ready. As you say, they probably are. And if they remove the AT&T SIM cards, then yes, they will absolutely not incur any AT&T charges.

Quick update: I forgot that the reason we have the "burner" phone is that my childrens' phones are still under contract with ATT and therefore NOT unlocked and NOT able to accept an international SIM card.

This is why, going forward, I will only spend money on UNLOCKED phones!

Most carriers will unlock a phone if you tell them you're travelling internationally. There usually are some restrictions, but they're usually not too crazy.

Don't know about ATT but T-Mobile has free International data program (for certain countries. I'm pretty sure France is part of it) along with no contract plans. Maybe something to look into.

I was just looking for myself for a trip to Mexico. There is an ATT Passport you can add - http://www.att.com/shop/en/wireless/international/global-countries.html#a

Base price is $30 and I was wondering if anyone has used this anywhere or in Mexico (We are headed to Cozumel particualrly)

So does this mean that I can use the sim card that I bought in February in France when I go there again in May?And, if I want to use Google maps, but also want to be able to use the phone I would need both data and phone, right? And then when we go to Switzerland a week later, then I would need yet another plan, right? (I know, I find this international phone stuff terribly confusing...)

@chroma2, We are skipping the phone and using Viber for voice. (When our oldest was in Berlin it worked well.)

Also, I do not know the details of the SIM card you purchased. Apparently some of the less inexpensive pre-paid ones you get at a Tabac do have time limit. Lebara? I am going to send them down to Orange and have them get one there. (Check, but I am pretty sure Orange carries over to some parts of Switzerland as well.)

We have used the ATT Passport plan fairly often but I find that it to be SO MUCH more finicky, and with more limited coverage areas, than just using the best local telecom provider.

We just spent some time in Mexico. If you have Verizon, there is a plan for Canada and Mexico. You can get 1000 minutes per month on your cell phone for around $15.00 for calls to and from those countries if you don't take the data plan. It works fine. For texts you can use Whatsap if you are in wi fi. Also if you have Vonage phone service at home, you can user their app on your cell phone to make calls anywhere in the world for free if you are in wi fi.