Free calls are now possible with SFR :

A new revolution for SFR. The operator announced today its proposal to include free calls to all mobiles in its range NeufBox. This decision will be taken into account from January 18 and will be included in the new offering neufbox "Evolution. "
SFR is trying to deal with its competitor which launched its Free Freebox new "Revolution" 14 December 2010. Free Freebox proposed a subscription with unlimited calls to French mobile phones and 103 free destinations and mobiles.