New technology has made it possible for VCO calls to be full-duplex, though I have not yet heard of it being practically applied. Phones specially constructed for VCO, such as Ameriphone's Dialogue models, feature a small display screen in addition to the handset and dialing buttons. There is no keyboard, though many of the phones have a button that sends "VCO PLS GA" to the relay operator, signaling them to switch to VCO mode. And while TTYs used to require the 45bps Baudot code to communicate, many now have a "Turbo Code" feature or can communicate in ASCII. Turbo Code allows for full-duplex typed TTY conversations, a concept that could be carried over into the VCO world.