Currently there are two approaches for obtaning contact information for a
target cell phone: (i) consulting a phonebook, (ii) manually exchanging
phone numbers upon face-to-face user contact. Both approaches have
their own limitations.
The following is a new abstract solution, a third alternative, a protocol
for "pairing" two cellular hosts:
Model of operation
1. The querier user types the target user's "human name" (as if he were
consulting a phonebook), or a pseudoynm.
2. The pairing request is forwarded to the target phone.
3. The query, along with the querier user's name, are displayed on the
target phone's screen.
4. The target user approves the request in real-time by pushing on the YES
button of the phone.
5. The two phones exchange their Mobile IPv6 home addresses, SIP URIs, and
establish an IPsec security association (using IKEv2).
The target user does not need to publish his/her private SIP URI and home
address (as recommended in  in SIP context). Cell phone users do not
publish their phone numbers today.
The users do not need to manually exchange their SIP URIs and home
addresses which are too long (an IPv6 address is 16 bytes long and random
looking, a SIP URI can be very long e.g. up to 30 characters and even more
with a random part for privacy).
The protocol also works in the absence of user contact, for example when
the target user's SIP URI is lost (loss of state, new phone), or this is
the user's first phone, and hence his/her contact list is initially empty.
Thousands of cell phones are sold everyday..
 Peterson, J., "A Privacy Mechanism for the Session Initiation Protocol",
RFC3323, November 2002.
Please note that this is an abstract to solution, I personally don't know
how to design it (or, which design might be the best one). I hope this would
of interest to the IETF. Comments appreciated either here or please
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