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Tape-spond was a form of correspondence used before the internet and inexpensive long-distance phone calls.
People recorded letters on cassette tapes and sent them to others in the mail. It was cheaper than a long-distance phone call.From A 2007 Interview with Nancy Kippax:
From a 1985 zine proposal request:...a two or three hour phone call from, say, New Jersey to California might cost somewhere over a hundred dollars or so. Multiply this by 5 or six calls and you can see what an enormous bill you’re racking up. Mail was, therefore, the method of communication for the majority. Trek fen gave a whole new meaning to the term “pen pals.” Sometimes letters were eight or nine pages long, defining characterization, discussing story premises, debating every aspect of the relationship we all loved. I corresponded with fans in England, Scotland, and Australia, as well as those in the states... another form of correspondence was taping. Employed by Laurie as well as others, they made audio tapes instead of writing letters. Long discourses were more easily made by talking rather than writing by some, so this became another early method of communication.
Help! We are two writers who are looking for an interested writer or writers to help us correct, complete a novel of 2000 pages. Writer or writers would share work, correction, profits of novel. No dirty smut or pix please. Cassette tape letters are welcome. 
- from Datazine #38 for the proposed zine "Star Trek: The Constellation Chronicles"