[maccoy]

You need to buy a new sim card.
I don't think you will find a sim card in the CDG airport but you can take a look at the "Virgin" Shops.
With your phone (it should be operator lock) you can only use a sim card by Orange or by a MVNO working on the Orange net: Virgin Mobile, Carrefour Mobile and Tele2 Mobile have a prepaid offer.
The "cheapest" one is Carrefour Mobile (39 cents a minute to France and 80 cents to the US) but you can only buy it in a Carrefour store (there is only one in Paris near to the metro stop "Porte d'auteuil" on the line 10).
The second cheap one, Tele2 Mobile has to be buyed online.
And the third one is Virgin Mobile (42 cents a minute - 27 with the XTRAJ offer that gives you less time to spend your money - to France and 85 cents to the US) that you can usually find in the bigger Virgin Shops (there is one on the "Champs Elysées") and in all "The Phone House" shops.

The cheapest MVNO works on the SFR net and is Auchan Mobile but you have to buy it in an Auchan store (there is one at the metro stop "La Défense" on the metro line 1 or the RER line A, in the "Quatre Temps" mall - and "La Défense" worths a trip...)
Your brother (and you if you decide to unlock your phone: you would pay between 10 and 20 euros to do it here in Paris) could buy this one.
It costs 39 cents a minute to France, Western Europe and North America.

You need any more informations?