Divelink makes a great underwater communications system for SCUBA divers. Check out their site and find info on the product and the names and addresses of dealers.
Fuji Ultrasonic Engineering of Hamamatsu City, Japan, manufactures underwater communications system for sports divers, called the FIT Phone. It's a compact and highly sophisticated system that consists of three models: Receive Only, Two-Way and Surface. Whenever you wish to talk, just push the button and you can communicate underwater. The system is also compatible with other underwater communicators.
SeaSigns of San Diego, California, presents dive signs for underwater communications which are based on American Sign Language (ASL), Signed English, and accepted diving protocol. The company offers videos, flash cards, specialty classes and consulting.
