OT Phone Blocking

AFAIK there is no way that the phone system 'knows' the origin number of a call. Yes, if the CallerID function is turned on, then the call number is transmitted as part of the call, but if it is not enabled, then that number is never available on the system.

My home phone system is Ooma, which allows a blacklisting feature, so I start by blocking ALL 800 numbers, then add as needed... I currently have about 36 numbers over and above the blanket 800.

The cell is a different story... on Verizon... limited blacklisting... so I add annoying callers to my contact list, but assign ring=silent ;-)

With a long pick-up time to voice mail this is pretty effective. ...Jim Thompson

I don't think that's right. Certainly someone with an 800 number knows the number of anyone calling. The phone system must have this information.

That is not correct. The number is transmitted by the phone system up to the last exchange, with an indicator telling if the originator wants it sent to the subscriber or not, and only the last exchange will actually filter the number when that is desired by the caller.

That is why it is not possible to have an app on your phone that tells you the number of such calls, but it *is* possible for the operator to offer a "block calls from this caller" feature even when the caller does not want his number revealed. They know the number so they can put it in a filter list.

(of course it is also possible for your operator to break the agreement and send the number to you even when the caller wants it to be hidden, but I don't think the large operators would do that)

I'm trying to remember what it was called, but there used to be some extra data in there that the phone company used for billing, that contained the originating number??

Does that still exist? If so, it might be possible to build your own decoder. ...Jim Thompson

On the trunks internal to the telephone system, yes. But this information is not transmitted to the user. (way in the past with in-band signalling such things were sometimes possible)

Must depend on the operator, and probably country then.

Certainly in Australia you have to have CallerID turned on at your number so that number is sent as part of the call data. Without that, no callerID is transmitted.

So a marketer can simply not have his callerID turned on, in which case nobody can discover his number.

If CallerID is on by default in the US, than IMHO that is a better system.

I see no reason why a callerID should ever be blocked. If you as the call originator block your ID, why are you making the call ? I can see no legitimate reason why you would refuse to identify yourself, whether by callerID or by voice within the call.

I know that tele-marketers exploit this, but why should we let them ?

CallerID is a function of the receiving end, no? It is top-left side. The data is sent by the called but it's blocked by the operator if you don't have CallerID. My cell phone can show the caller if I pay $3/month. It must be a super-callerID sort of thing because I get the phone number unless it's blocked by the sender. I don't know if it shows this information, too, but if it doesn't it really has no purpose.

That can be done here, too. You can't block your phone number from a toll-free (AKA 800) number. They pay for the call so get the information.

Again, telemarketers can block it. It can easily be spoofed, as well. I get junk calls from random cities across the country.

Battered women?

Because they pay Ma for the privilege.

There are a number of valid/legitimate situations where callers would prefer to have that option.

Dob-in-a-dealer is one. You want to let the authorities know who to shine the spotlight on at 04:00 but the concern about repercussions if your identity is attached in any form is entirely valid.

I also have information which I would like to pass anonymously to another "investigative party" (NOT media!), but if my identity were connected to that information/inquiry my life could well be foreshortened.

In the US it is a cat and mouse game. A caller can block his number, but you can reject calls that have blocked there number. I think this is all workable through the phone system and doesn't require any special equipment. But it was at least a decade ago that I looked into it all, so it may have changed now.

I would like to be able to block my number when I call 800 numbers. But that is a different system than the caller ID thing and can't be blocked. I think it is because the 800 numbers are paying for the service. lol

This is how you see it as the end-user. What happens in reality is that when you "block your callerID" it is still sent along with your call through the telephone system up to the exchange of the called party, but it is accompanied by an indicator that says "the originator of this call wants to be anonymous".

When the called party subscribes to callerID, he will normally get the information, but in the case this indicator is on, the exchange will not send the info. However, it still has it available!

E.g. at the ISP where I subscribe it is possible to get telephony over IP (I don't subscribe to that service) and they offer caller blocking by keying *351# during or just after a call. When you do that for an anonymous call, they block the number they have available. You never learn what that number is, but it cannot call you again. Other anonymous callers can still call you. This proves that they (as a telecom operator) have the calling number or another unique identifier available even for anonymous callers.

Also, there are certain services here (like the emergency number) that always have the calling number on their screen (including reverse lookup information) even for anonymous calls and unlisted numbers.