Given that we can have purely numeric domains, i.e. 131500.info, why not have domains that map to our mobile phone numbers for personal use?
What's the point? For one, you can give out your public mobile number instead of your website, since it is much easier to communicate numbers than domain names. This can be used to communicate other information that is difficult to convey by voice, e.g. emails, skype names, etc. A simple website at $your_mobile.mob would overcome all these.
This obviously has privacy implications, and as such should be entirely opt-in.
Any such system would need to be regulated, ideally controlled by carriers. A custom TLD like .mob would probably be a good idea too. One must also keep in mind however that such easily predictable domain names will be targeted by spammers.
Cheers,Steve