You can buy stamps and change money at the mobile post office at the ancient site, Monday through Friday from 8am to 2pm. This office is sometimes open on weekends and after 2pm, but don't count on it. There is a pay phone (not always in service) near the mobile post office.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.