Free use of phone (iphone 6) without line using only local Wi-Fi hotspots?

So my mom gave me her iphone 6 cause she doesn't use it anymore and there's a crack on it.
the line(verizon) has been disconnected, but the phone still says verizon on the upper left screen
(i'm noob on phones)
i hear there are ways to keep using the phone as long as you have a local Wi-Fi (at home or at work) using apps? Like apps that lets you have a number that receives texts or calls too? As long as you have Wi-Fi connection.
and i'm assuming the apps will keep working even without a subscription.

also i was hoping to switch to a prepaid thing, no idea how. I'm clueless with phones.

my last phone was like 8 years ago. Where all you could do was dial numbers and send texs. No idea with these apps and stuff.

Yes, there are apps that give you a virtual phone number that other people can use to call/text you. I haven't used them in some years, but the last one I used was TextNow.

Now, I don't know how well the audio quality on calls would be; you would need to test that out yourself. These apps work without an active phone service, but as you know, will only work on Wi-Fi.