Bouygues, and everything was active within a few minutes. It was the third store I went to.

SFR said that their prepaid system had been down for several days and they had no idea when it would be back up.

Orange flat-out refused to sell me a prepaid SIM for an iPhone because the guy insisted that my background apps would burn through my data allowance "in five minutes".

Bouygues was happy to help. Their network was perhaps a bit wonky - in the Luxembourg Gardens, for example, my phone showed full 3G signal but had no data connectivity - but overall it was fine. Speeds were good and coverage was fine throughout the parts of France I went to (Paris, Brittany, Normandy, and Champagne). I had to buy data in 200 MB chunks through their automated system or online. It worked fine, and they sent a text when I was out of data.