OK gentlemen, I concede it was not in the GPO/BT lexicon!
I first became aware of the term in this context about 25 years ago, but it looks as if it was an American expression (and therefore probably adopted in many other countries).
Here is a US patent document from 1974/75 that mentions ringback tone in the context under discussion 58 times, and at least once without the word "tone".
http://www.google.co.uk/patents/US3920913
It wasn't my intention to subvert anyone's understanding of telecoms terminology, even less to rewrite history, and I apologise if I gave that impression.