But from next February, a call to even the police or ambulance will become so complicated it requires an instruction sheet.

CapTel, the captioned telephone handset used by 4000 Australians who are deaf or hard of hearing to link into the National Relay Service, will not be supported when a new provider takes over.

The service is currently provided by the Australian Communication Exchange, which has an exclusive licensing deal to use the CapTel technology.

The contract was worth $90 million over five years.

But last month the federal government signed a new three-year deal with Concentrix for $66 million.

Under the deal, users of CapTel must switch to a teletypewriter or TTY in order to receive captioned phone calls.

Former communications minister Mitch Fifield pledged last April that no one would be worse off as a result of the changeover.

But Mr Brimson said the teletypewriter was a poor alternative.

The teletypewriter screen is far smaller than the CapTel, and has no scrollback function, Mr Brimson said.

The only way to review a conversation is to print it once you've hung up.

The process is also more convoluted than with a CapTel.

CapTel users simply dial an outbound number into their handset and are connected to the National Relay Service, where operators use a text-to-speech device to transcribe up to 130 words per minute.

With a teletypewriter, users must first call the National Relay Service, then plug in the outbound number. The service can only relay around 45 words per minute.

Mr Brimson has been given a nine-step instruction sheet on how to call emergency services through the teletypewriter, which he believes is too many in a stressful situation.

Under the new system, users would dial 106 instead of 000.

They have to ignore the prompts on the screen for fire, police and ambulance, and instead wait for a relay officer to pick up the phone.

"Older people especially will have difficulty enacting the steps under duress, and if you're contacting the emergency services, you're under duress," Mr Brimson said.

Mr Brimson also said users had been encouraged to use a computer to access the National Relay Service, or send a text message to another obscure number.

"Imagine needing an ambulance at night, wake up, turn on computer, insert password, connect to internet, go to [the National Relay Service] website, log on with password, ask for emergency services, be transferred to 000 operator, ask for ambulance, wait for relay officer to transcribe 000 operator's questions, et cetera. This will be difficult when under stressful conditions," Mr Brimson said.

His wife Jean is concerned it will make Mr Brimson's life more difficult and more isolated.

"It's a simple thing but it's life-changing in so many ways," Mrs Brimson said.

A letter to Mr Brimson from the assistant secretary of the consumer safeguards branch in the Department of Communications, Kath Silleri, said the provider of CapTel in Australia was "unwilling" to work with Concentrix.

But AccessComm, the company which distributes the technology in Australia, said that was untrue.

"Neither AccessComm or Australian Communication Exchange owns or has any rights to the technology, we simply operate the platform which delivers speech to text," AccessComm spokesman Tony Bennetts said.

"Neither organisation has the ability to transfer the technology and the government is aware of that."

But a spokeswoman from the department said AccessComm was not helping with the transition by refusing to provide user information.

She said the cost overruns in recent years made the agreement with the incumbent provider "unsustainable".

The tender put out for the National Relay Service in 2017 was capped at $22 million per year, despite the service costing $31.2 million to deliver in 2017-18 and $32.2 million the year before.

Ms Silleri told Senate estimates in February this was because the department "had an understanding" the service could be delivered cheaper.

The Australian Communication Exchange contract had already been extended twice because a "value-for-money proposition" could not be found, Ms Silleri said.

She would not be drawn when asked whether it was fair to say no one could deliver the service for that price.

The vast majority of users of the National Relay Service appear to favour the CapTel handset.

The latest quarterly report showed 73 per cent of inbound calls used the handset this year. Internet relays accounted for 15 per cent of inbound calls, while all other technologies combined - including teletypewriters - made up the remaining 12 per cent.

The department spokeswoman said their tender process was "technology agnostic" and focused on the needs of National Relay Service users.

"CapTel was not excluded from this process," she said.

The spokeswoman also said while CapTel would not be supported from February, "whether CapTel is provided on a standalone basis is a matter for CapTel".