Disposable Phone Numbers

by Moshe Yudkowsky

A friend recently asked me how many email addresses I had; her family thought she was a geek because she had six. I guess I'm a little more geeky: I have over one hundred eighty email addresses. Every time a company asks me for an email address, I generate a new one just for that company and arrange for incoming mail to show up in my normal inbox (I've automated this to a single command line in Linux). If the company abuses my email address by sending me spam, I disable the email address. Disposable email addresses guard my privacy.

I'd certainly like the same system for telephone numbers, because sometimes a company will get hold of my phone number and never let go. (Horror stories deleted; fill in your own.) Internet Telephony provides a solution. One reason Internet Telephony is a revolutionary innovation is that IT takes the ability to establish telephone numbers away from a central authority and gives it into the hands of anyone who wants to terminate calls. Telephone numbers become an unlimited commodity instead of a precious — and lucrative — resource.

Until IT becomes ubiquitous and all telephones can dial using the "sip:foo123@example.com" syntax, I've devised an alternative scheme to achieve disposable telephone numbers: use a single telephone line, but assign each company its own extension.

I've written a demo Disposable Phone Numbers application in CCXML, VoiceXML, and Java, running on Voxeo's free Prophecy server. As each call comes in, the caller is asked for an extension number, which the caller provides using spoken words or touch tones. The extension goes to local Java servlet, which does a check of the extension number (it should be a database lookup, but my prototype just checks against a short internal list). If the extension is valid, the call goes through; if the extension is invalid, the application drops the call. If anyone is interested in hearing the pre-alpha -- and the user interface is just barely good enough at the moment -- they can try it by calling the demo number at +1 312 957 6568, which terminates at a computer on my desktop. At the moment, the only two valid extensions are 3350 and 8932, and all calls are dropped. If there's enough interest I'll release the application as open source.


2006-09-21 16:32:51
If telemarketers figure this out, they could automate autodialers to find a valid extension. Are you doing anything like allowing only a certain number of attempts from any callerID for a specific time? Or you could devise an extension generator that creates extensions with internal checksums. Granted this would make extensions longer, but it would also make it much harder to guess a valid one.
Moshe Yudkowsky
2006-09-21 20:49:29

Good questions. First, I plan to add a random digit to the valid extension to make it harder to guess. I thought of a checksum, but it occurs to me that any checksum algorithm could be compromised, while a random digit cannot. Since the numbers are in a databse anyway, random digits are safer than checksums.

Your other question is about automated guessing. The application architecture allows me to gather statistics about who calls, and I can generate blacklists and other systems to prevent abuse. Internally, the application keeps a score to determine whether or not to permit the user to keep trying to say the extension. I expect that as I pursue development, I will end up with procmail-like rules.

Thanks for your input!


2006-09-22 10:12:34
I'd definitely be interested in something like this. Can you briefly explain the setup and hardware so I can see if this is something I'd be capable of doing? Is it just a computer with 2 modems and software on it? This is definitely a project I would enjoy playing with in my spare time.
Russ Meyers
2006-09-22 10:18:18
if($ani =~ m#@blacklist#){
2006-09-22 10:27:37
Can something like this be used for international calling?
2006-09-22 10:30:18
These already exist but not in America. When I was in HongKong recently I was able to get a free mobile phone from the hotel. But they charged some insane amount per minute rate! All I did was go down the street to a cell phone shop and got a new sim card. I pre-paid a certain amount and got a phone number with the sim card. I used that card instead of the one the hotel gave me. Then once I was done with my trip, I put back the hotel's sim card and threw away the one I purchased. I wish the pay as you go systems here were as advanced and easy to use.
2006-09-22 10:32:07
I didn't go to the extreme of extensions, I just used Asterisk, and callerid. If the caller doesn't provide a callerid they are informed via a recording that they must turn their callerid on to call this number and are hung up on. If a caller with a particular callerid starts Phone spamming me they can be put on a blacklist and never allowed through.

Dane Kouttron
2006-09-22 10:40:08
I would be very interested in viewing your source. it is a great idea
2006-09-22 10:41:38

what's your setup for that?? is it just a computer with 2 modems and software? i hear about this stuff but haven't seen a from scratch how-to or setup instructions.

2006-09-22 10:49:13
I'd be interested in this can you explain how it works?
Moshe Yudkowsky
2006-09-22 10:59:58
I've applied for a Sourceforge project (that link doesn't work yet); I'll put a note here when the site is turned on.

The idea of using Asterisk and a whitelist/blacklist is certainly feasible. But I perfer to know how the person got my telephone number. Did I give it to them on their web site? Did they get it from a conference organizer? Did they purchase it from some other company that I gave it to? Using a Disposable Phone Number lets me associate the caller (and their ANI) with the disposable number.

Moshe Yudkowsky
2006-09-22 11:04:02
As for getting started: that's a bit beyond the scope of this little article. However, you can turn any Windows PC into a small speech recognition/text-to-speech/telephony system by downloading the Voxeo package that I reference in the article. They have some tutorials, and I run a Voxeo Prophecy platform developer web site.

That will let you terminate incoming calls, make outgoing calls if you make a deal with a SIP service provider, and use a softphone. If you want to interface to "classic" telephone equipment, you'll need an Analog Telephone Adapater, an "ATA." Again, beyond the scope of this article.

2006-09-22 11:10:57
it may be beyond the scope of this article, but you've given me some things to google to get me started :)
2006-09-22 12:51:11
I like the idea. But, it's very rare to find a phone extension value able to be entered on a form that you don't want to leave your real number at.
2006-09-22 13:20:21
Let me know what you think of My Ad Box for those without technical skills.


Moshe Yudkowsky
2006-09-25 07:26:52
"MyAdBox" provide an interesting service, but it's not quite the same. And at $10 per disposable telephone number, it's qute expensive.
2006-09-27 22:19:29
It sounds interesting. It will be great if you can release it under an open source license.
Moshe Yudkowsky
2006-09-28 05:07:55
Sourceforge is having a bit of trouble, but as soon as it's sorted out, I'll post the URL of the project.
Ariane Avril
2006-10-01 03:47:14
Great idea!!!! I'm very interrested. It has been a long time that I was looking for that.
Very smart.
Joel "Jaykul" Bennett
2006-10-02 09:50:21
I'm deffinitely interested! Please do release the source...
2006-10-06 14:39:06
This sounds like a good idea. I recently came across another site that lets you get as many disposable extensions as you want. Also provides numbers in about 10-20 cities. Check it out at http://www.talktrust.com
Oh by the way, they have other applications beyond just the disposable numbers and it all seems to be FREE at the moment.


Moshe Yudkowsky
2006-10-09 07:10:38

Thanks for bringing TalkTrust to my attention. Very secretive company, however; no names on the web site, which is quite puzzling.

2006-10-17 05:20:34
why not use temporaryinbox.com instead?
Moshe Yudkowsky
2006-10-17 07:32:45
temporaryinbox.com doesn't offer nearly the flexbility that I want. With 180 addresses that all end up in the same inbox, I can easily track who is spamming me, turn individual boxes on and off, and I can maintain long-term service -- some of my dispoable addresses have been in use for as long as three years.

By the way, don't get me wrong: temporaryinbox.com (and Mailinator, another similar service) does an excellent job at what they're attempting to accomplish. My requirements are for go beyond temporary. The addresses have to be disposable -- perhaps "accountable," "plentiful," "durable," and "zero-cost" captures my requirements more fully.

2006-12-28 03:03:00
Iam starting a new company with little money
I thank this will be a big help to get started
please release the application soon.
2007-02-15 22:59:54
I discussed this idea of disposable email addresses and phone numbers on spamcop.com forum 2-3 years ago and people didn't seem to undrstand power of disposable addresses and phone numbers.
I'm glad to see understanding people here. Disposable addressing is the right way to fight with spam and Bayesian spam filters is wrong. Same idea can also be used to fight with credit card fraud - disposable credit card numbers (already provided by MBNA bank).
I use disposable addressing services for email - emailias.com, use disposable credit card number from MBNA, but still can not find any suitable disposable phone numbers service that would not charge per phone number (extension). All virtual pbx services seem to not understand that need. I would be very happy to see reliable service for disposable phone extensions paying low monthly fee, but high per minute charges.
Moshe Yudkowsky
2007-02-16 02:28:30

I just record the news, I (generally) don't make it!

However, I agree: I also want to have extensions that won't expire; in fact, I'd like to have a database that contains per-contact information -- the phone number and email address I gave that individual, as well as any other information that I've provided and what it was.

I'm Alexy
2007-03-07 20:52:08

I totally agree with your requirements: "accountable," "plentiful," "durable," and "zero-cost".
They are right and I'm sure exactly what many people really want.
"Disposable" or temporary" word is wrong, the main goal is not to dispose contacts, but preserve them for many years so any address that you give to your school friend will remain valid for 100 years just because no one spammer can abuse it.

Please implement your idea ASAP, I will be your first customer.
I looked at Tossable Digits, it sucks, they expire after 30 days of no use, I didn't even want to try that useless service. It looks like whoever implemented Tossible Digits is not capable to keep primitive table with 3 fields:(phone, extension, forward phone) and unlimited number of records on the server. Hey, whoever does this extremely hard thing:) first providing similar other functionality will be the winner of all permanent customers including me. I'm ready to prepay for 10 years of service, are you ready to accept my money ?

2007-03-07 20:58:08
Another suggestion: when you forward the phone call, please send extension number instead of caller id.
Caller id is almost always unknown these days, which makes it useless, but extension id disclosure is something that doesn't depend on caller and recipient will always know who is calling.
With that feature your service will become twice more useful.
Moshe Yudkowsky
2007-03-08 02:54:34

You bring up a very interesting idea: that "disposable" phone numbers help keep your contact list active over the years.

Right now I know non-technical people who change their email addresses when they can no longer endure the spam they receive. I expect the same will happen in the future for phone numbers as the problem of "voice spam" grows. If phone numbers were disposable, it would be possible to drop compromised numbers and retain the others.

2007-09-09 01:55:25
http://www.StealthNumber.com offers anonymous unlimited flat rate calls, voice mail, caller ID, call forwarding etc.
2007-09-09 15:30:12
This is very interesting... I'd like to learn more. Where can I get more information (for non-technical people)?
Moshe Yudkowsky
2007-09-20 07:38:33

I'm not certain what other information you're interested in. Can you contact me directly? You can find contact information by clicking on my name.

Josh Russak
2007-10-24 08:11:23
I can't even begin to say how amazing it is that I found this article. I am currently working on a concept that will drive more traffic towards these "Disposable Phone Number" companies. I am curious if it is worth starting my own DPN service or to partner with an already existing company and work off a CPA basis?

I'd like to discuss this product with you more in depth and see if it's worth my time and money. With the current mobile trend and SMS-Advertising, I feel there's a strong future ahead with such a product.

I look forward to getting in touch with you whenever is most convenient. Let me know when we you are available.

-Josh Russak

Josh Russak
2007-10-24 08:12:21
I can't even begin to say how amazing it is that I found this article. I am currently working on a concept that will drive more traffic towards these "Disposable Phone Number" companies. I am curious if it is worth starting my own DPN service or to partner with an already existing company and work off a CPA basis?

I'd like to discuss this product with you more in depth and see if it's worth my time and money. With the current mobile trend and SMS-Advertising, I feel there's a strong future ahead with such a product.

I look forward to getting in touch with you whenever is most convenient. Let me know when we you are available.

-Josh Russak