We arrive at CDG on a Sunday around 2pm and would like to get a SIM card with data (have unlocked phone). Any advice on where to get one? Would prefer to get one of the big 3 (Orange, SFR, Bouygues), but all the company stores I've searched look like they're closed on Sundays. We are staying near the Louvre. There seems to be conflicting posts on whether or not one can be gotten from CDG... Thanks in advance!

None of the top four companies sells SIMs at the airports. Relay stores will generally sell SIMs for companies such as Lebara or Lycamobile. The price is typically 10€ with 5€ talk time credit.

Orange has a store on the Champs Elysées open on Sundays.

Oooh, that's good to know. One hiccup - I just looked at the Orange site and for that store it says:
Travaux - Du lundi 01 juin au mercredi 09 septembre (http://agence.orange.fr/6380-boutique-orange-paris-08)

Does that mean it'll be closed? I'm there in July... I tried looking at other shops especially in the tourist areas, but don't see others that are open on Sundays...

Is it too much to hope that Orange would arrange to have another location open on Sundays if they're only store that is goes under construction?

Do they sell data SIMs at a branch of Fnac? Their Champs-Elysées store is open Sundays from 12 to 2345.

I hope you won't mind awfully if I hijack your thread to ask, why not just pay for a month's international plan from your cell carrier? I always wonder this when reading these threads about SIM cards--please enlighten me!

I use AT&T in the US and their international data plans are very pricey. $30 for 120mb / $60 for 300mb / $90 for 800mb. We will also be traveling outside of Paris and using our phones as GPS while we're driving, and that can suck up a lot of data bandwidth.

T-Mobile US gives their subscribers free international data, but I'm not with them. Their coverage where I am is not great.

What's the best way to find out if FNAC sells SIMs and which ones? Can anybody help?

Thank you for the explanation!