Really? I can't say I have experience building such a system, but to me it seems the solution has already been built: fast off-the-shelf DNS servers, using phone numbers as virtual (sub)domains.

My experience is in the context of payments - when charging someone's payment card, check whether it's one we've issued and just run it as an internal balance transfer rather than run it through Visa (read: free). When doing the whole "build fast, iterate quickly" thing, it's easy to forget about such optimizations, especially when it's a relative edge case and works just as well if you leave it alone (arguably better, since there's less conditional logic in the code)

So by "network" I more meant database (i.e., network of users).