One of the most common questions asked by people not familiar with this topic is why real-time, character-by-character based text communication, also known as interactive text or conversational text, is needed in the first place in a world where email, SMS, instant messaging, chat and other text based communication methods are readily available.
The short answer is that real-time text is an alternative to voice telephony, whereas message based systems such as SMS, MMS or email are non-conversational, supplemental communication systems. Instant Messaging sits somewhere in between.
Hearing people use a variety of communication systems, both conversational (voice telephony, IRC, video conferencing, etc.) as well as non-conversational ones (SMS, email, message boards, etc). The method used to communicate depends on the context, as well as on the abilities and preferences of the users. In other words: sometimes SMS will be sufficient, whereas in other cases, there is a need to talk directly to the other party, for instance using voice telephony.
This principle of having various modes of communication available and choosing an appropriate one depending on context and abilities is a key factor in understanding the need for interactive, real-time texting (text telephony) for deaf, hard of hearing and speech impaired people. As such, text telephony is specifically meant to be the text equivalent to voice conversation for deaf, hard of hearing and speech-impaired people. To make it an equivalent of what voice is for hearing people, text telephony must offer equivalent features in terms of conversationality as voice does to hearing people.
Having a voice conversation with someone is characterised by a number of specific features:
One of the crucial features of text telephony is that it offers a character-by-character based interaction. So, everything that is typed will appear immediately on the screen at the other end and vice versa. That feature is extremely important in making text telephony equivalent to what voice is for hearing people, especially the ability to make relay calls (explained further below). Relay calls can not be made via message based systems such as SMS or email. Even Instant Messaging is unsuitable due to high latencies and delays as a result of line buffering the text.
Deaf people do not only communicate with other deaf people. They need to communicate with the rest of the world, just like anyone else. In fact, the ability to communicate continuously and effectively is extremely important if one is to be a fully enabled citizen in the Information Society: in employment, in education, in social life, entertainment etc. To enable text telephony users to communicate with voice users, there exist relay services, like for instance RNID Typetalk in the UK or the relay services offered by Sprint and MCI in the USA. Current text relay services use human operators that read all the text that the deaf person types to the voice user and types back to the deaf user what the hearing party says. The usability of these relay services decreases rapidly if the interactivity diminishes. Research has shown that character-by-character, real-time interactive text is necessary to use the relay service, otherwise the interactive nature of the conversation disappears almost completely.
No hearing person in their right minds would propose to abolish voice telephony because of the existence of other communication channels like Instant Messaging (IM), SMS or email. As the above has made clear, it is not about either one or the other. People use different services side by side, depending on need and context. In other words: it is a serious misunderstanding to assume that any text-based form of communication can be used to replace voice for such users. As the above hopefully explains, that is not the case at all (just like IM does not replace voice telephony for hearing users, but rather offers an additional mode of communication) and it is imperative that a proper, mainstream interactive text based communication system is available for the millions of deaf, hard of hearing and speech impaired people in the world - if these user groups are to be fully enabled and fully included citizens.
Deaf, hard of hearing and speech impaired people require a text based, character-by-character, interactive, full duplex communication system as well as widespread access to terminals that support it, similar to what voice telephony offers to hearing people in terms of functionality, interoperability and availability.
As long as hearing people need and use voice telephony, deaf, hard of hearing and speech-impaired people will need real-time, character-by-character, interactive text. As hearing people are now using voice telephony services not just on landline terminals, but even more so on mobiles and increasingly over the Internet, real-time, character-by-character, interactive text must be available to deaf people on those platforms as well.