I had not had a cell phone at all for myself in over 18 years. A new iPhone 7 was donated to me in the past year and Vonage became useless to call DR phones. I HATE Apple as a company, but free is free. It is the first ever Apple product, and my first ever smart phone, that I own, but as I said, I didn't pay for it. I tried to avoid ever having another cell phone, but that effort finally failed
The iphone7 could not be unlocked, so a special Turbo-SIM un-blocker is in on top of an ALTICE SIM card in it. Works just fine and dandy that way.
For US calls I use the Google Voice App, which has no issues for me and is free for me to call and receive US calls. 5G? I might worry about that, or not. Likely not.