If you activate an android phone first (needed anyway to earn silver since there is no flipphone app) and then email support@cellnuvo.com they might do it. No one has tried as far as I am aware. They let iphones on that way but an iphone app is coming soon. You'll have to ask them if it is possible. There is no way you can directly sign up using a flip phone since the app is required for initial activation.
Maybe cellnuvo support could chime in if around please.
If he doesn't use much then tello is probably better for a flip phone. Or TPO if you want unlimited talk/text for $7.99+ tax.
Second question:
How many CellNUVO account can one person have?
I have my own CellNUVO account.
I'm signing this second account for my uncle under my Billing address. I will have to earn Points for him. He doesn't know how to use smartphone.