Be careful about what is termed "unlimited" mobile from orange and SFR. Both mean "unlimited" upto what they consider fair play, then you are cut off until the next month. Fair play on a mobile is way below what you would expect, so check the very very small print.
If you only need limited access between arriving in France and getting the land line connected consider the local Mediatheque. Many towns and villages have, inside the local library, several computers connected to the internet which are free to use for periods of up to 2 hours per day. They are usually closed Sunday and one day in the week, and sometimes only open morning or afternoon.