In my last post I mentioned two services, Trapcall and Spoofcard, that exploit some technical features of Caller ID. The post provoked an irate but interesting comment, to which I wrote a lengthy response.
Caller ID arms race
Keeping your phone number or even your email address secret kind of defeats the object of having a phone or an email service, which is to communicate with people. From this perspective your phone number should be easily available to anybody who might want to call you. Hence phone books.
But the phone book has taken a beating in recent years. Most numbers are not listed because they are cellular numbers and the mobile service providers don’t publish phone books. Plus many consumers keep their land line numbers unlisted. I don’t know why mobile numbers don’t appear in directories – I presume some form of laziness on the part of the providers. But I believe that the reason people request unlisted numbers is for privacy. Paris Hilton or Brad Pitt could legitimately expect tiresome intrusions if their numbers were published. Less famous people may affect similar concerns.
A new service avaliable in England takes the issue one step further. Now to avoid intrusive phone calls you have to keep your name secret, too. An article in the London Times on June 9th described a new service from a company called Connectivity Ltd.
It will function along the lines of an old-fashioned telephone operator: users will call the service and ask to be connected to the mobile phone of a person. The service calls that mobile phone and asks for permission to connect the call.
My point about keeping your name secret was hyperbolic. You don’t need to keep your name secret because you can opt out of the directory. But this solution shows that you don’t really need to keep your number secret either, and could get a similar degree of privacy protection without giving up the benefit of reachability. Your service provider could keep a list of numbers that have called you, and a call from a number not appearing on that list could offer you the options of accept, reject, whitelist, blacklist. Blacklisted numbers would never ring again, whitelisted numbers would ring through without asking. I don’t know who currently offers such a service, but in the teeming world of VoIP services I presume somebody does.
Another manifestation of the idea of privacy through secrecy is Caller ID blocking. It has always been my policy to reject calls with blocked caller ID, because it seems kind of rude to block it. The caller knows who they are calling, so why shouldn’t the answerer know who is calling? The caller blocking his ID seems to be saying “I know your number, but I don’t want you to know mine.”
To defeat such rudeness, the call recipient may turn to a service called Trapcall, which purports to unmask blocked Caller IDs.
Trapcall seems like a nice way to render symmetrical the information of the caller and callee, but it becomes problematical in cases where call anonymity is essential. An example of this is a battered wife shelter, where a resident may need to call her husband, but does not want him to discover where she is.
In the spirit of an arms dealer supplying weapons to both sides in a conflict, the people behind Trapcall offer a service to defeat it.
Both Trapcall and Spoofcard rely on the fact that PRI subscribers have greater access to the signaling information than do regular POTS subscribers. In particular, the number of the calling party can be conveyed to the called party by two different methods: ANI and Caller ID. Even when Caller ID is blocked, calls to an 800 number disclose the ANI. As I understand it the rationale here is that the person paying for the call is entitled to all the information associated with it. This seems like weak reasoning to me, especially if the caller is paying for Caller ID blocking, and consequently has a reasonable expectation that their number will not be disclosed. Caller ID contains whatever the originating switch happens to put in it. For POTS lines the service provider puts the originating subscriber’s number unless he subscribes to Caller ID blocking. PRI subscribers like Spoofcard can program their PBX to put whatever they want in this field.