What's the Verizon plan called?
You are fortunate that you didn't waste money trying Virgin Mobile, here it doesn't work any better than Cricket. Both are so oversold and slow they can't even open a web page and I suspect Millenicom would be just as bad on Sprint and wouldn't want to spend $220 just to find out. How did you get a plan running on Verizon? They don't offer anything using Verizon on their web page, just Sprint.
What's interesting is that a friend warned me about Cricket. But I was seduced by the prospect of getting high speed internet for $40 a month, with no overages. So I signed up and ultimately came to regret that decision, as Cricket's network is woefully inadequate. For the speeds you get, I can see them charging maybe $20 or $30 per month. But their current price levels are just insane. They charge $55 a month for 5 GB of data. You can go on Verizon's site and order directly from them and get 5 GB for $50. It's actually cheaper to use Verizon, despite the fact that Cricket has a significantly worse network and, according to logic and reason, Cricket deserves to be priced cheaper. Of course, the big difference is that Verizon requires you to sign a contract, whereas Cricket allows you to pre-pay. As does Millenicom.
You asked about Millenicom's service plans. They actually have 5 plans at the moment:
3G/4G Hotspot: $80 a month and uses Verizon's 3G and 4G networks.
Advanced Plan (which is what I have): $60 a month for 20 GB but requires the $99 purchase of the modem. Uses Verizon's 3G network.
Unlimited Plan: $70 a month and it uses the Sprint's 3G network. They say "unlimited" but it has a 50 GB soft cap.
Bring your own device plan: Same as the unlimited plan. Uses Sprint 3G.
Standard plan: $60 a month for 5 GB. Uses Verizon 3G. Doesn't require purchase of the modem.
Hope this answered your question. Thanks for the comment!