I appears that at the same time Verizon changes their service plans Millenicom will no longer be offering the 20GB/month plan.  It appears that if you have an existing plan you will be able to keep it, at least for now.

This was my online conversation with them.  The hardware not being available is likely just a convenient smoke screen.

Well, I guess the 20GB plan from Millenicom is indeed gone. Here was my online chat with them.

08:57:21 Thank you for contacting us. An operator will be with you shortly...
09:00:51 Josh: Hello! Welcome to our online support. How may I help you?

09:01:20 Visitor: I was interested in your Adavanced plan that has been listed as 20GB/month for $59.99. I no longer see this plan offered. Is there a mistake on the website or has this plan been discontinued?

09:01:32 Josh: We had to pull the advanced plan, there has been a shortage of devices (modems).

09:02:12 Visitor: Is that permanent or can I still provide my own modem that will work with that plan?

09:03:21 Josh: the only modems that work with that plan was the modems we were providing, if you have a millenicom device that was previously on the advanced plan you can activate it again, other modems will not work

09:04:14 Josh: due to the lack of devices there is an early bird special on the 3g/4g hotspot plan, if you click learn more on that plan you will see that special

09:04:33 Visitor: I see. No, I would be a new user. So will there no longer be any plans at the 20GB level?

09:05:20 Josh: no untill we get new devices, however like i said there is the early bird special on the 3g/4g plan, please take a look at it

09:05:45 Visitor: Also, the previous plan did not work with 4G. Does the 3g/4g work on 4g in a 4g area?

09:06:07 Josh: yes