I make almost all calls using wifi.
By make all calls via WiFi, do you mean through a WiFi calling feature on the phone itself, or and entirely separate service, such as Google Voice? If it's a WiFi calling feature through the phone like what T-Mobile offers, you're still billed minutes used.
It's also worth noting that depending on the TracFone plan, texts and mobile data are dinged as credit against your minutes as well. That's one of the big problems with their proprietary handsets with the built in credit counters.
Beyond that, if you're not using phone built-in WiFi calling or any texting at all and mobile data is turned off? Good luck with that! Changing your number won't solve anything, and will likely make your situation worse. The pool of numbers that TracFone holds and the policies in place for recycling those numbers and putting them back in service so quickly brings with it a whole other world of pain. I tried that once nearly a decade ago, the number they gave me had been out of service less than three weeks. Friends of the previous number owner were convinced I stole the guy's phone and proceeded to harass me and leave death threats on my voicemail. Had to file a police report. Why didn't I just change my number? There's another nightmare that doesn't even get into the billing issues and the terrible customer service both I and my wife experienced while there, either.
When TracFone works, it just works. But when you run into problems?
There's a lot of reasons why of all the MNVOs out there, I don't recommend anything owned by America Movil. I don't talk much about these experiences, as I prefer to deal with the concrete issues. Bad terms of service, vendor lock-in, bad support, billing issues... instead of getting personal with the tales and first hand experiences. I've tried diligently to not directly talk about them in such negative light beyond just the facts of record.... but sometimes, you just gotta be honest about it. There's a reason why there are so many complaints out there for the company. End of the day though, those experiences contributed to my wanting to write the communications guide in the first place. Help people find less terrible providers on a budget.