I think about buying a SIM card in Iran for local phone calls. What's the best/most popular operator and does it cover all Iran? Is it possible to work with a "prepaid" system so I can add credit whenever I need it?
You can buy a prepaid Iranian SIM card from “Irancell” , Rightel ir MCI (Hamrah Avval) companies which are available everywhere from the airport to the supermarkets and the prices starts at around 6 USD.
Check the cheapest Iran budget tours.