SIP telephony enables highly dynamic scenarios, but phones usually go through tedious setup procedures. NFC Tags may make all this dynamic. In addition, they could add vital security measures.

Many people carry a mobile phone anywhere they go. This certainly helps our reachability, but many also prefer to be out of reach once in a while. For those who use a mobile phone chiefly for outgoing connectivity, but with the wish to talk over a "real" phone, a desk phone is ideal... with the exception of its static location, perhaps.

Now imagine a SIP phone with an NFC interface. We might swipe our NFC Tag (or NFC-enabled phone) by it to indicate that we intend to be reachable on that phone, and another time to stop that. The simplest mechanism for doing this would be using a vCard on our NFC Tag, but we might actually provide credentials such as a Kerberos ticket to enable the phone to register more properly; we would probably have to enter a PIN on the phone to enable doing that.

Further imagine that a call comes in, and that it is encrypted to a Kerberos ticket that we supplied. A phone supportive of this could now require us to present our NFC Tag once more before we can answer the call. This procedure would avoid that anyone else could answer (DoS danger) or communicate (information leak) using our identity.

Much of this is yet to be designed. SIP telephony still has battles to fight regarding end-to-end encryption, and adding Kerberos may or may not make things any easier.