It's not at all clear to me that Mobile IP would be viable at the scale of a modern wireless service provider. It amounts to routing all traffic to/from the mobile device through a machine on the network of its "home" IP address. Without some fairly invasive routing shenanigans, this would be disastrously bad for users traveling far from their home network (e.g. a user gone on vacation).
Not that it matters, really. As far as I'm aware, there were never any substantial deployments of this protocol.
I was more responding to OP's tongue in cheek comment about government assigned addresses
I still remember how I felt when I sent that first invoice. I was beating myself for not sending the invoice every week in the process, yet there I was with what I thought was a giant bill.
For context, the company that commissioned the work paid over $100k for that single page (I was in the email chain). It was part of a wider campaign that involved a whole lot of work, interviews, filming, celebrity appearances, etc. I just checked and the page is still up!
Ps: it involves that reliable car company, news paper, and mothers.