I am still using my basic Core Ooma device, it still works perfectly, and I pay nothing whatsoever in any kind of fees for unlimited calls to US and Canada. Sound quality is great!
If you can get a hold of the ORIGINAL Core device (they are still out there) or Core with Scout (kind of an extension of the unit) they are grandfathered in at NO FEES-EVER. I happen to have a brand new one, still shrinkwrapped, with the Core and Scout Device, and I have confirmed with Ooma that it will always be no fees. I don't know why I have it, just saw it on Ebay one day and bought it for $200, as others there were going for much more due to the no-fees thing. So. it sits in my closet.
Also, they have told me that if I ever want to "upgrade" to the Telo, my no fee deal will be transferrable to the Telo. No reason to do so in 4 years, as mine is working perfectly, as it always has.