I think you probably know this, but you could have a 2nd number wth the premier service.

Then you could port your primary number out to google voice. Then, use an obi device to maintain a voip line service to your home phones to which the ooma is currently hooked up.

With the number at google voice, you could have it forwarded to or simple ring to your cell phone number (which is basically what you are currently doing now) There are no fees for this service other than the 30-45$ for the initial obi hw purchase.. google continues to renew the GV services for free but it could go up to maybe 20-40$ a year.

then drop premier with ooma, keep the new number and your ooma will still function fine just with the one number.

You'd then be able to use the ooma for calls (if you hooked it up as well) and you could still use the ooma app, albeit I think for only 250 minutes a month from your ios device. ATT WIFI calling works very well pretty much everywhere.

I don't think you can stop the ooma and re-start it later and keep the same terms (no fees or taxes) so once it gets officially shut off, that plan cannot be recovered. You'd have to sign up for a new plan which would most likely have the fees.

Ooma currently has an undocumented program for current HUB owners or legacy Telo owners on no fees. you can move up to the latest Telo 2, and negotiate no fees for 3-5 years. . after that the at the time fees would go in place (anywhere from 4-7$ a month depending on location)