It is frequently stated that Hawking used a DECTalk system, but in fact he did not. He used a Speech Plus CallText 5010. They sound similar because DECTalk and

It is frequently stated that Hawking used a DECTalk system, but in fact he did not. He used a Speech Plus CallText 5010. They sound similar because DECTalk and CallText were both based on the MITalk work of Dennis Klatt. The full story can be found here: https://computerhistory.org/blog/how-dectalk-gave-voice-to-a-genius-engineering-stephen-hawkings-wheelchair/