I just received an email from “Freedompopinvite.com” that said my free (Sprint-based) account had been upgraded to a $3.99/month plan. If I wanted to stay on the free plan I would have to click on a link in the email. Nevermind that the email was flagged as junk by my email service, but clicking on a link from an unknown sender?
Researching the web, I found this discussion on BestMVNO and a related thread on SlickDeals.
I logged into my Freedompop account, saw that I had been “upgraded”, and then typed in the URL my.freedompop.com/sprint-plan. That gave me the button to return to my previous free plan. I have another free plan that hasn’t been “upgraded” yet, but I’ll keep an eye on it.
ETA: If you have a free plan, make sure you have at least a $5 credit on your account before doing the downgrade. Some BestMVNO posters mentioned being charged $20 to do the downgrade - that might be because they had a $0 balance.