, this will turn the button from green to gray. if hardware tty is on, toggle this off as well. faq what is rtt calling? rtt stands for real time text; this assistive technology lets you use text to communicate during a phone call right from your iphone or cellular ipad. what is tty...
with AT&Tlodging a complaintagainst T-Mobile and Sprint for launching Wi-Fi calling without getting the appropriate waiver that would allow the companies to use RTT