Phone to use while driving in France

Here's a link to the various AT&T plans https://www.att.com/shop/wireless/international.html.
You can select a plan (prepay) for a data, texting & a better per minute rate or simply opt for pay-as-you-go (I seem to remember ~ $2.00 USD per minute which may suit your emergency only needs. Additionally, they've a specialized customer service/sales team that can assist you with evaluating the options.
BTW - On several trips I've selected the $60 (prepay) plan with $.50 per minute calls, ~150 MB of data, and unlimited texting - it's worked well for me (I've a family member who needs to call daily so I budgeted for five minutes of calls per day).

I used the least expensive plan, never made a call, and still got $5 of voice charges extra when the phone kindly "delivered" voicemail messages when I went out of airplane mode to use my texting and data. It was my credit card company asking about charges another family member made back in the states. Certainly not a big deal, but just be aware that if you have your US phone, you can get voice charges even if you don't use the phone. I was a bit surprised. Otherwise it all worked as expected and I had plenty of texting and data for my minimal needs. I will probably do it again for the next trip coming up soon.

If you want to stay connected at all times, you could consider renting a wifi hotspot. Using wifi you can FaceTime with other Apple users, send iMessage texts to other Apple users, or use apps like Skype to make calls. Rick tried out renting a hotspot and described his experience, "You can now travel with a tiny hotspot that frees you from messing with the gobbledygook of getting online while on the road. Telecom Square rents a handy little unit about the size of four fingers called a Mobile Wi-Fi Hotspot that works virtually everywhere in Europe (and most of the rest of the world too). While it’s not cheap, the convenience, reliability, and luxury of being online anywhere and anytime in my travels makes it a great value for a traveler like me." Read more about Rick's experience with it at http://blog.ricksteves.com/blog/ricks-consumer-report-on-a-wi-fi-hotspot-rental/.

js,

As I stated in my other reply in your other Thread.....

"As you're just using it for emergencies, you could leave it turned off unless needed. If you have to turn it on to make a call, be sure to switch the cellular data off."

If you won't be using the phone extensively, the AT&T international roaming plan will likely be the most cost effective and easiest option. Unless you've chosen a data option with the international roaming plan, leave the "cellular data" switched "OFF" so you don't incur any unwanted charges. That will still allow calling and texts.

One point to keep in mind however is that if you travel with your home number and the phone is switched "On", you may still receive calls from friends back home that don't realize (or have forgotten) that you're travelling. Some of these calls may be received in the wee hours of the morning, which is a darn nuisance. YOU will be paying for each of these incoming calls, billed to the nearest minute at whatever the applicable rates are on the roaming plan.

Thanks everyone. I am leaning towards using the AT&T international plan.

If your phone is unlocked, or can be unlocked, consider buying an inexpensive local SIM card.