

Nah, I don’t think there’s a lot on IPv6 in that book. I think OP’s concern is valid. Accessing devices at home isn’t unheard of. The amount of smart home stuff, appliances and consumer products increases every day. And we all gladly pay our ISPs to connect us and our devices to the internet. They could as well do a good job while at it. I mean should it cost extra to manage a static prefix, so be it. But oftentimes they really make it hard to even give them money and obtain that “additional” service.
I think if you use a SIP provider, they’ll have an app or a description on their website how to connect with third-party software. Just install it on a device you take with you, and configure it as per their description. Examples for Android SIP softphones are Linphone and Baresip.
Other options: you have a AVM Fritzbox at home and install their app. Or you set up an entire PBX like Asterisk or FreePBX or one of the other ones. That’s rather complex and involved.