And there's the answerback code. Lots of companies do not have a computer or a modem. The world is bigger than we thought. Telex is easy and familiar. Most companies have a computer with a modem, but that doesn't mean employees are comfortable with them.
Telex is the status quo.
Some business sectors are still grouped around networks of firms with established routines of sending and receiving telexes each day. This penalizes any individual firm that tries to upgrade ahead of whatever ponderous association decides things by consensus for that industry. Last year at Manchester Airport in Britain, I missed the last train home to my mother's village because of flight delays. Last month an American building consultant friend in Budapest was baffled to get a fax from DHL asking him to send a telex to Hungarian Customs to release a package. He had to go to a hotel to send one.