I purchase an unlocked cellphone. I will be arriving Paris through the Charles De Gaulle airport. Where is a good place to buy a SIMM that will work in France and Germany?
Grady,
I don't have specific advice on locations to purchase a SIM in Paris, but a few other comments.
Since you'll be travelling in two countries you might also consider a SIM from one of the "travel cell" companies such as Cellular Abroad or Call In Europe. If you purchase a SIM in France, you'll be charged higher roaming rates when you use this in Germany, so you'll be topping it up more frequently. The travel SIMS will provide consistent rates in several countries.
Whichever option you choose, be sure to check the rates carefully so that you have a clear idea on your costs.
Cheers!