Brian Gaff used to work at Telecom Tower in London (formerly the Post Office Tower). I need to get a bit more info, but basically he found a load of these in a storeroom; they'd obviously been there since the early 80s when the telco operated their Prestel service....this modem sat under the Speccy and allowed you to access both the Prestel and Micronet 800 dial-up services that were popular at the time, as well as any other viewdata-type service that was around.

Obviously since they were stored they're unused.