Leo Bicknell: Lastly, you've assumed that only a "smart phone" (not that the term
is well defined) needs an IP address. I believe this is wrong. There are plenty of simpler phones (e.g. not a PDA, touch screen, read your e-mail thing) that can use cellular data to WEP browse, or to fetch things like ring tones. They use an IP on the network.
Alternatively, Verizon is planning to build an all-IP NGN architecture in the near future, or is at least providing for the possibility of building one. Mobilkom Austria, for example, has done a deal with Fring to put their SIP VoIP client on handsets and serve their voice traffic over IP. In that case, you'd need IP addresses for all the people who use VOICE. You can do ringtones and the like through USSD...but there's no escape from voice.