The Hologram Nova arrived. It cost $49, and then I had to pay some sort of import tax.
I connected it to a Raspberry Pi, and tried to install the software. The error messages led me to think that I'd need to upgrade the version of Raspbian, so I did that, and tried again. This time, the Hologram software installed.
I went to their web site at https://hologram.io and registered the Sim that came wiith the device. I chose the free option. That went well. Then I created a devicekey, and then I tried it out.
hologram send -v --sms --devicekey xxxxxxxx --destination +44yyyyyyyyyy "This is a test"
xxxxxxxx is my devicekey, yyyyyyyyyy is my mobile number, with the leading zero removed. And after about ten minutes of so, the text appeared on my mobile phone.
So now I can log into the Pi with the Nova and send texts to anyone with a mobile phone.
Evil laughter ...