The 1957 newspaper clipping from here reads:
Headwork in the Garden
The chic hat Paul Johnson of Jacksonville, Fla., wears while gardening may not keep off the iun, but it will bring in all local radio stations. The one-tube radio headset operates on two dry cells to enable him to keep up with his favorite programs while doing outdoor chores.
Erkki Huhtmao gave a great keynote “History of Mobile Technology” at ISEA 2004 (the website iis sadly not online anymore), with a general overview of the history of mobile media. Some of this has been published in in receiver. I keep collecting examples for a music and sound history of mobile media. Hopefully I’ll have time to put it together in a coherent form one day. If anyone has more examples I’d love to hear about them!