The service has been restored and appears to be working fine.
Meanwhile, WhatsApp and other mobile-messaging services have cost phone carriers an estimated $32.5B in lost revenue from texting fees.
WhatsApp's messages are sent via the Internet and are free once the application has been downloaded and a data plan has been paid for, while traditional text messages are sent via the cellular network.
Separately, the WSJ profiles the role of former Google employee Neeraj Arora in WhatsApp's negotiations with Facebook. Arora is WhatsApp's one and only marketing manager, human-resources head, publicist, and business-development chief.