We will be passing through FRA in a few weeks and will have lots of time to kill in the airport (an understatement - we have a 7 hour layover between flights on two separate tickets). One task I'd like to accomplish during all that free time we will have in the airport is buying SIM cards for our phones/tablets.

We won't be staying in Germany other than our (admittedly long) transit through the airport; our actual destination is Corsica (France), so we will want SIMs from a carrier that works outside Germany, across the EU (when we fly home, we will be stopping for a few days in continental France before going by rail to Switzerland for a day before catching our long flight home). My understanding is that generally SIMs from just about any EU country should work (equally well?) across all of them (and in non-EU Switzerland, too) so I assume that's not going to be an issue.

I'm guessing that in this huge airport there will be plenty of shops selling phone SIMs. Can anyone recommend a decent one? Thanks.