I'm registered as an auto-entrepreneur (profession libérale), waiting since June 2012 for the carte vitale. It's still in the works and could take months until I get it. However, through some detective work and then some kind advice from a medical lab technician, I was able to quickly obtain a letter from RAM called an "Attestation d'ouverture des droits", which proves I am covered by the French system and allows me to access medical services as if I had a card. Wish I'd known this months ago, could have saved a fortune on the private emergency medical insurance I've been carrying.
Unless you are in the Ile-de-France region, I found out that auto-entrepreneurs in our category need to deal with the RAM office for professions libérales - Provinces. It is in Bourges, in the département of Chér (18), in the Centre région. I have the telephone number, perhaps I should not post it here, but you can contact me if you wish. The office was very helpful over the phone and I got my letter two days later - and I'm far from there, in 06, so a visit would have been difficult. Hope this is of help to you.