Letting you know that I have it working! My problem seemed to be a bad SIM card connection. I removed it, cleaned it and reinstalled it and things started working.
The DIGI XBEE3 LTE Cat 1 radio seems to work great now using my Hologram SIM card and the APN “hologram”.
We are using it in the transparent mode where the radio establishes a TCP/IP connection to our server via the Internet. The only problem we have is that communication seems to be slow to start after a long period without any traffic. But the problem is not insurmountable.
We experience a 1 – 2 minute period after power-up while the radio gets connected to the cellular network, and then everything works great!