On Mon, 17 Dec 2012 23:11:55 +0000, Graham. wrote:

You can get secure messaging services. Another employer I worked for
used "Cognito" which allowed for delivery and read receipts. It was
integrated into the ticketing system, so we could work out how efficient
the engineers were - they hated it as we could tell exactly when they
opened a message. I think it was overlaid on the GSM network.

COGNETO!
I had one of those in a previous life and I've been wracking my brain
for years trying to remember what it was called.

I think we had them before we got Band III radios installed in our cars.

Ah, the dangers of hearing a word, and never seeing it written down