Right now the three mobile companies offer prepaid SIM cards for AR$0 to AR$5. That's less than US$2.

You can Buy a SIM card wherever you see the words Personal, CTI or Movistar. In the town center you can find at least one or two stores per block.

Calling INTL is pretty expensive. The trick is to use a "prepaid calling card" that you can buy at any newstand or "kiosko" (little/big drugstores), or even in the stores I mentioned above. Ask the teller which card gives you most minutes to your destination.

Have a nice trip!!