> my device is moving from one cell tower to the next, getting a new IP address every few minutes

You're pretty much never getting a new IP at every cell tower.

> Then I get to my friends house and his router is gonna block unestablished connections so you better call me soon.

PMP can solve that.

> Because relying on your users to have stable IP’s

Not a stable IP, but some kind of stable identity. Like a DNS name. That can be provided by someone like Apple, or Google, or whoever. It doesn't need to be ultra-centralized by only a single thing controlling it.