Samsung GALAXY S6 User Manual page 82

 Your phone's TTY mode is set.
Note: When enabled, TTY mode may impair the audio quality of non-TTY devices connected to the
headset jack.
Warning: 9-1-1 Emergency Calling
It is recommended that TTY users make emergency calls by other means, including Telecommunications
Relay Services (TRS), analog cellular, and landline communications. Wireless TTY calls to 9-1-1 may be
corrupted when received by public safety answering points (PSAPs), rendering some communications
unintelligible. The problem encountered appears related to TTY equipment or software used by PSAPs.
This matter has been brought to the attention of the FCC, and the wireless industry and the PSAP
community are currently working to resolve this.
Phone App 71