> Yes. My ISP will rent me a single IPv4 address for $10 per month.

At that price point you can get a small vm, but if you have a dedicated server you want to use on-prem, 10$/mo seems like a reasonable price.

> Or I can use DHCP, where my IPv4 address can change at their whim.

Check the dhcp.lease to make sure, I used to think that, then I looked at the dhcp lease and the IP was being reserved for up to 48 hours of disconnection. I went years without it ever being released.

Phone operators won't necessarily transmit this information to you, the true ISP operator is the DHCP server. Not only is it more knowledgeable, but DHCPd has no incentive to upsell you, just provides you with what it is configured to.

I'd even go as far as checking if you can send parameters during the dhcp lease request, maybe you can request a longer lease on the IP.

There's a right way to do things, it's not trivial to discern from the wrong way to do it, but once you see it, you notice that you lose almost nothing, it's not like the 'wrong' way is simpler, it's just 'wronger', all the way through. I guess the reason they persist is sunk-cost fallacy, the businesses and people that went with NAT then developed STUN, and then they developed ICE, and then they develop Tailscale, every time you need to invent a bigger spade to dig you out of the hole and into a deeper one.

Or you can just use IPv4. But aghast, you have to pay 10$/month (or learn DHCP)