I quite like the idea of my cell phone being an ID card for 2 reasons
1. if I lose it, the government can help me find it - i think we should demand mandatory tracking of id cards for this reason.
2. there's a really strong incentive for people not to nick it as it is a way worse crime than just nicking a phone.
all sorts of benefits accrue from this, including really accurate driver (rather than car) based congestion charges, and all sorts of useful tricks in emergencies (instead of broadcasts on trains saying "is there a doctor on board" one would just ask the doctor to go the the right carriage).
why on earth would any honest people object to these advantages just because of some sentimental attachment to some fictional notion of privacy?