BBC News has raised privacy concerns about the speech-to-text translation service used by Telstra.
Telstra's speech-to-text service is designed and operated by British company SpinVox, which claims to use a speech-recognition technology to convert voicemail messages into short messages (SMS).
The technology caught the interest of Telstra and Optus at Mobile World Congress in February - with Telstra chief technology officer Hugh Bradlow telling iTnews at the time he "now listens to one in 10 voicemails, because I'd rather view them as a text [message]".
It was trialled by both carriers and sold by Telstra.
The BBC claims SpinVox over-stated how many messages are translated by machine.
It said some were translated by call centre staff in Britain, South Africa, the Philippines and Egypt.
The BBC story quoted workers in these call centres who said all SpinVox messages - some personal or of sensitive information - were translated by humans.
SpinVox said the report was "incorrect and inaccurate".
The company said it used human translators for training purposes. The translation system only sent messages to human agents when it couldn't decipher a message, the company said without revealing how often that occurred.
"All speech technology requires training," it said. "This requires humans to correct and inspect some audio and text to provide the system with corrections. SpinVox not only does this real-time but in total security through anonymisation, encryption and randomisation.
"Agents working in a live environment have no knowledge of customer, individual, product, market or use - the data is fully locked down."
SpinVox said it was "absolutely clear in our communications that humans form an important component of our learning system".
And it said it shared this information with its carrier partners.
"SpinVox has been through due diligence with some of the largest carriers in the world," it said. "Following their due diligence and audits they have gone on to sign contracts with SpinVox."
Australian Privacy Commissioner Karen Curtis told iTnews that Australia's Privacy Act "would not prevent the involvement of humans in voice-to-text conversion, providing that the organisation is complying with the requirements of the Privacy Act".
"The Privacy Act requires organisations to notify people about why their personal information is being collected and what it will be used for," Curtis said. "In the case of voice-to-text conversion, good privacy practice would be for customers to be notified that people may be involved in the conversion process."
Telstra's marketing materials for speech-to-text fail to mention human translators, saying that translations were "automatic".
It's only disclaimer was that Telstra "can't guarantee that the message will be correctly translated and we are not responsible for the content of the message".
But within the terms and conditions of its speech-to-text service, Telstra said that "in some instances, we may use a third-party agent to assist in the translation of individual words or small portions of a voice message".
A spokesman for Telstra told iTnews the carrier is comfortable that "in the majority of cases the translation of voice messages to text is fully automated".
"But in the small number cases where human operators are required to translate parts of a message, agents have no knowledge of the customer," the Telstra spokesman said.
The UK Information Commissioner's Office said its Data Protection Act "does not prevent SpinVox from using people, rather than machines, to translate audio messages into text".
But it asked SpinVox be "clearer about the likelihood that people will be used to translate messages".
"This is particularly important if customers are using the service for transmitting sensitive or secure information," it said.
SpinVox said it stores data in secure facilities in Britain and adheres to the ISO 27001 international Information Security Standard.
"SpinVox has successfully managed millions of conversions, and has no history of breach of security," the company said.
An Optus spokesman confirmed the carrier remains interested in working with SpinVox to launch a speech-to-text service.