TTY modems by using a software-based decoder for TTY tones. Same can be done with such software using a computer's sound card, when coupled to the telephone line. In the UK, a virtual V.18 network, called TextDirect, exists as part of the Public Switched Telephone Network (PSTN), thereby offering interoperability between textphones using different protocols. The platform also offers additional functionality like call progress and status information in text and automatic invocation of a relay service for speech-to-text calls. Cell phones Many digital cell phones are compatible with TTY devices. Many people want to replace TTY with real-time text over IP (RTT), which can be used on a digital cell phone or tablet without a separate TTY device. New technologies As TDDs are increasingly considered legacy devices, with the emergence of modern technologies such as email, texting and instant messaging, text from TDD are increasingly being sent over Text over IP gateways, or other real-time text protocols. However, these newer methods require IP connections and will not work with regular analog phone lines, unless a data connection is used (i.e. dial-up Internet, or the modem method of multiplexing text and voice that is done on a Captioned Telephone hardware handset). Because some people have no access to any kind of data connection, and it is not even available in some parts within many countries, TTYs are still the only method for analog landline text phone calls, although TTYs include any device with a suitable modem and software. Other devices for the deaf or hard of hearing In addition to TDD, there are a number of pieces of equipment that can be coupled to telephones to improve their utility. For those with hearing difficulties the telephone ring and conversation sound level can be amplified or pitch adjusted; ambient noise can also be filtered. The amplifier can be a simple addition or through an inductive coupler to interact with suitable hearing aids. The ring can also be supplemented with extension bells or a visual call indicator. Etiquette There are some etiquette rules that users of TTYs must be aware of. Because of the inability to detect when a person has finished speaking—and the fact that two people typing will scramble the text on both ends—the term "Go Ahead" (GA) is used to denote the end of a turn, and an indication for the other person to begin typing. Sample conversation Caller A: