Consider this, your browsing the web on your phone with your unlimited data plan and a site requires you to register or login, whats easier to type on the phone? http://rwvhp.com or 07714110660 (my old mobile number), I know different people will prefer one over the other.
It is possible and heres how, VoIP uses ENUM and e.164 to work out the domain name from the phone number. This could also be used to work out the OpenID of the user with very little work and as far as I can tell is just as secure as OpenID as both can suffer from attacks via DNS.
I’m basically just throwing this out there to get some feedback and as a note to myself.
Vincent is a self-confessed geek, who's day job is as a Rails developer, outside of work he likes to play with home automation gadgets. He resides in Newcastle upon Tyne.