Wednesday, September 15, 2010

When Blocked Caller ID Calls Are Not Really Blocked

You may think turning off, or blocking, your caller ID can make you anonymous to the person you are calling. Well...... it can but..... not really. Linda Scott out at the Education Development Center in Newton, MA paased along a link to a service called Trapcall. This service can be used to unmask blocked and restricted calls, allow users to blacklist harassing callers, and can also record incoming calls. There is no software to install and the service will work on mobile phones from AT&T, Verizon, T-Mobile and Sprint.

Here’s a piece on how TrapCall works from a 2009 Wired article:

TrapCall takes advantage of a loophole in Caller ID blocking that’s long benefited corporate phone customers: Namely, calls to toll-free numbers are not blocked, because those calls are paid for by the recipient.

TrapCall instructs new customers to reprogram their cellphones to send all rejected, missed and unanswered calls to TrapCall’s own toll-free number. If the user sees an incoming call with Caller ID blocked, he just presses the button on the phone that would normally send it to voicemail. The call invisibly loops through TelTech’s system, then back to the user’s phone, this time with the caller’s number displayed as the Caller ID.

The caller hears only ringing during this rerouting, which took about six seconds in’s test with an iPhone on AT&T. Rejecting the call a second time, or failing to answer it, sends it to the user’s standard voicemail.

And, here’s a short video from HousholdHacker demonstrating the service:

If you think this stuff is not very popular take a look at the YouTube view counter for the video - almost 2.4 million views as of today.

In my 2003 book Introduction to Telecommunications Networks I wrote the constitutionality of caller ID has been repeatedly challenged in court with people having three major concerns:
  • The right to be left alone
  • The right to be free from unreasonable searches or seizures
  • And, the right to not be subjected to unreasonable government intrusions
Privacy works both ways for me. I don’t think I’ve got much to hide so don’t worry too much about having to block my caller ID. If I do have concerns about my number getting out I’ll just use another phone with a public number. If someone does call me from a blocked number, I typically just let it go to voicemail.


Toll Free Number Information said...

"There is no software to install and the service will work on mobile phones from AT&T, Verizon, T-Mobile and Sprint..."

That means it's a extra paid service from these carriers right?

Gordon F Snyder Jr said...

There is a monthly TrapCall fee. See the website for details.
Your provider service needs to have conditional call forwarding enabled for it to work.
My intention is only to help people understand blocked calls are not necessarily anonymous.

Lisa researching call blocking said...

It's a pretty cool feature. I rarely answer my phone if I don't know the caller's number anyway.