Why do you say that? It only takes hearing them once.
IIRC, Letterman’s show muted part of the dialing when Letterman was calling someone because previous to the muting, people were picking up the phone numbers from the TV show. I think he may have even said so on the show.
I think that neither a machine nor field experience is necessary – a little trial-and-error with tones will do.
I wouldn’t go that far. It’s true that most people have a good sense of relative pitch–that is they can easily distinguish between to slightly different tones when heard side-by-side. However, few people have an accurate sense of absolute pitch; the ability to identify a particular pitch without reference to another. This is sometimes called “perfect pitch”. Although it’s very easy to distinguish one button from the other when you listen to them one after the other, but try identifying a particular one at random on its own, and you’ll likely find it more difficult than you think.
Anyone with a good sense of musical intervals could do this. And if you had a mediocre musical ear, you could cheat a bit on earlier model touch-tone phones by pressing two adjacent keys. This would give you the fundamental tone for that row or column of keys, yielding a complete interpretation of the keypad for the solo keypadist.
And as recently as 10 years or so ago, coin-operated phones could be fooled by modifying a radio shack tone dialer to emit a series of “nickel tones” (nothing like the keypad tones), and… well, you can guess the rest. This doesn’t work anymore except as an extremely elegant way to broadcast “hey, come arrest me for wire fraud” to the US secret service. Even if it did work, LD rates are so low these days that the benefit would be negligible.
I know several musicians who can do it as well, quite effortlessly.
Hey, some people are really into DTMF Melodies:
http://www.dialabc.com/sound/music.html
http://www.dialabc.com/links/phone/dtmf.html
http://2u2u2u.michaelv.org/telephone/
Foaming Cleanser Re: Posting #15
Yes, I remember doing that back in the old times (rotary phone days). To me it was very hard to tap out a 7 digit (and now it would be 10 digit) telephone number. I took the lazy way - 10 taps - “Hello Operator I’m having trouble reaching 867-5309 could you try that for me?” 
It will still work to this day. A phone line that can accept tone dialing will always be able to accept pulse dialing.
Case in point - my brother bought a “dial” phone with the “dial” a ten key tone pad. I put the phony electronic dial in the message box underneath. I then found an old phone and took the rotary “action” out of it and installed it where the tone keypad was. If you leave the electronic keypad’s setting on “tone”, you can use either the dial or the keypad. Here’s the best part - If you want you can “dial” a number by using the rotary dial for the 1st digit, the keypad for the second digit, back to the rotary dial for the third and so on.
Just thought I’d share that. (And yes, my parents are very proud).
No you wouldn’t. Not anymore than you would have to with a portable tape recorder in your car. It’s not that sinister of a device.
Who needs DTMF decoders or perfect pitch? If you just want to be a creep and harass the person the radio station called, you only need to have an audio recording of their dialing and play that back into a phone.
The phone system doesn’t care if you’re sending it tones by pressing the phone’s buttons, a tape recorder, portable dialer (these used to be popular for storing those absurdly long MCI / Sprint long-distance access codes for use at hotels that only had rotary phones) or a plastic whistle from a box of cereal.
- I memorized the DTMF tones as a youngster 20 years ago. It wasn’t hard at all.
- Owning a DTMF decoder is neither illegal nor immoral. Though it could be used for illegal purposes. On par with owning a knife.
- DTMF tones can be recorded and played back to call the previous number. (Or re-enter the previously entered credit card if you’re a bad person).
Open in another window on my computer is the audio recording program Adobe Audition, which has a DTMF tone generator, with a numeric keypad you click on to generate the proper frequencies. It also has a DTMF filter, which will filter those frequencies out of a recording. I’m not sure under what circumstances you would need to do that, but there it is.
So it is not illegal to own a device that will generate or decode DTMF tones.
Answering the side question:
Yes you can still dial a number by tapping the switch-hook. I guess it is a lot easier to ask SDMB than to do the experiment. 
In fact, you can mix and match DTMF (tone) dialed digits with pulsed digits. I did this for a few months: I picked up my phone to dial, and threw a static spark from my finger to the first digit I touched. (4). This took out the 1-4-7-* column, but the remainder of the keypad continues to function. I got quite adept at manually pulsing the digits that fell in that column.
Note that you can still pulse dial a phone company line, but probably can’t pulse dial many private phone systems that serve modern companys. (which have mostly replaced the “PBX”)
DTMF decoders not leagle? Hardly. They are the cornerstone of voice mail systems…how else do you suppose they know when you “press one for english?”.
They have also been used for years by hams (Amateur radio operators) for remote control functions, as well as for monotoring autopatch activity.
We radio communications systems implementation and monitoring fans (ok, ok, scanner guys, if you like) and radio amateurs use DTMF generators and decoders for all sorts of things. For example, we might use the DTMF pads on our handheld radios to program changes or access codes on two-way repeaters. Your local fire station might use DTMF tones to open the doors to the fire house when they return from a call. Utilities use DTMF tones for all sorts of telemerty and remote control applications.
Here’s a sample (.wav) from KB9UKD’s great data signals sample page:
DTMF Speedcall recorded from water company telemetry.
There are software programs that decode DTMF tones also. I can’t find the link at the moment but a program called Wintone decoded DTMF very well.
I forgot there’re also DTMF decoder kits available. I know of at least 2 ‘stand alone’ DTMF decoder intergrated circuits that only require standard off-the-shelf external components to get a working decoder going.
More DTMF decoder boards for all sorts of projects:
http://www.dschmidt.com/dtmf.html
You’re missing the point entirely. The person who was curious could have done that, sure. But then other Dopers (like me) who had never even thought of such a thing wouldn’t have learned something new. That’s why we’re here, remember?
By the way, how many clicks do you need for #, 0, and *?
TJdude825 If you read my previous posting, you would see that 10 taps are for zero. The * and the # - well you’re on your own. (How did the # come to be called the pound sign? The only time I had ever seen it used as a pound sign was in archery. Doesn’t everyone think “number sign” when they see the # ?)
Kevbo - nice to know that someone else has learned you can alternate pulse and/or tone for making the same phone call. “Dopers” are an interesting bunch of folks. Heck, now I’ve learned that the “fast tapping” method of phone “dialing” may not work on company phones.