Area code 939 is an overlay for area code 787 in Puerto Rico, introduced in 2001 due to the increasing need for new numbers on the island. It shares geographic coverage with 787 and serves all major cities, including San Juan, Caguas, and Carolina. With the implementation of 939, ten-digit dialing became mandatory throughout Puerto Rico. The 939 code is typically used for newer mobile and internet-based lines. It helps support Puerto Rico’s growing telecommunications infrastructure and digital economy. Though newer, 939 is becoming more common and complements the established 787 in modern communications.