Scitec 2510E Red Single Line Emergency Desk Phone Hearing Aid-Compatible Handset ADA/HAC compatible. Handset Jack - Modular jack to connect coiled handset cord from handset to telephone. Ringer Volume - Adjusts ringer volume to LOW or HI. Located on the bottom of the phone. Data Port - Provides access to the telephone line for optional connection of modem, fax, or answering machine. Volume Switch - Volume control switch on the handset steps through the three available handset volume levels Normal to Medium to High