BBC News website age & disability correspondent
Software has been developed which enables deaf people to have real-time text conversations using a mobile phone.
The new software enables text conversations in real time
But the charity that has created the service says some mobile operators have yet to fulfil a legal obligation to make their services accessible.
The Royal National Institute for Deaf people (RNID) says only Vodafone has a relay service that uses the technology.
Landline users can already make such calls using the Typetalk facility.
Relay services allow a deaf person to make and receive a call via an operator, who turns the voice part of the conversation into text and relays the deaf person's text replies into speech.
Pressure on operators
The RNID's new software effectively extends the facility to people using mobile phones which are now an everyday part of most people's lives.
The charity says it will dramatically improve the ability of deaf, hard of hearing and hearing people to communicate in real-time.
Mobile network operators are now being urged to provide the software for their customers.
Nokia Communicator 9210
Nokia Communicator 9300
Nokia Communicator 9500
Sony Ericsson P900
Sony Ericsson P910
The application can be used on any modern mobile handset, and allows character by character text communication of unlimited duration.
"It has taken innovation in the voluntary sector to deliver this software," said RNID new technologies director, Guido Gybels.
"It's now time for operators to make sure that all their customers can access real-time text communication."
The RNID says that with more than 57m mobile phone subscribers in the UK, they are now an essential tool for anyone who wants to be a fully enabled citizen.
Like Vodafone customers, BT Mobile subscribers already have access to a text relay service which uses the RNID's technology.
BT Mobile says the Nokia Communicator 9210 is one of a number of compatible handsets.
T-Mobile says it already has a text relay service.
"Customers can use the RNID Typetalk service with BT's Relay Assist," a T-Mobile spokesperson said.
The company says it has recently launched an enhanced service which enables customers to make real time text/voice calls.
O2 says its subscribers can access the BT text relay service with the addition of a portable text phone that connects to their mobile handset.
One such device is the Textlink 9100 made by Sensory Communications.
Some mobile operators have yet to provide the service
Weighing more than 500g, this may well be taken on holidays or business trips but a deaf person is unlikely to take it with them to the pub.
A company spokesperson said O2 was committed to improving accessibility, already offering a range of mobiles with "qwerty" keyboards.
"We comply with our regulatory obligations and continue to research new features and services," the spokesperson said.
Orange customers also have access to a relay service, something the company introduced just over a year ago.
But like O2, people wanting to make voice/text calls need to use additional hardware.
One of the key advantages of this, according to Orange, is that it has a larger keyboard than would normally be found on a mobile phone.
Orange says it has investigated a number of potential options - including the RNID's - but prefers to stick with the existing technology for the time being.