On my Sprite bottle, it tells me to look under the cap for a code, and then send a text message with that code to find out if I’ve won. But it’s only a four-digit number. How can you send a text message to a four-digit number, unless every possible carrier in the US agrees to process that number?
Bingo!
A few years ago they decided to allow shorter phone numbers (4,5,6 digits IIRC) but only from devices such as cellphones, not from regular telephones. I’m surprised no one else has answered this yet. I’d find a cite, but I have no time right now. Sorry.
(Try the “search” function. I asked this exact question a while back in reference to the voting on American Idol.)
And isn’t it only text messages that can be sent to that number? I’ve seen any number of ads that say ‘text whatever to 123456’. I wonder what would happen if you phoned one. Odd that I never thought of it before.
I just looked on Fido’s website, and they list a number of short codes to text to. Send a text message to 93284 (WEATH) containing your city name and get the weather forecast. I know this works; I’ve done it before. But I tried phoning the number and got an error.is
You can now send text messages to landlines as well, at least from my carrier (Fido). The system calls the landline number and reads the text message. 
Nothing. The phone system will be waiting for the rest of the seven digits. That’s why fewer-than-seven works only from cellphones, and other such devices.
“Such devices”? What’s different about them?
Major stuff: On a regular phone the system is designed for a certain number of digits. If your second and third digts are both “1” (like 411 or 911), then right after the third digit, the system takes your numbers and tries to connect you. If they’re something other than that, it checks the first digit. If it was something other than “1”, the call goes through after the seventh digit. But if it was a “1”, it waits for eleven digits (1 + area code + seven digit phone number).
All the above is only for most places in the USA, and there are other rules too, but I hope you get the idea.
Cell phones work differently. It takes any number of digits, and then does nothing until you press “send”. When you press “send”, it sends whatever you entered. Which can be any number of digits. I live in an area where the “1” prefix is required whan any area code is used. No more of the 10-digit calls like in the 1980’s and prior. But I once noticed that the 1 is NOT needed on my cellphone. As long as it has the 10 digits, it doesn’t really need the “1” prefix.
I hope this helps.
Well, I had called 93284 from my Fido cellphone. 
But it didn’t work; I got an intercept message about “this number is a ten-digit local call and must be dialled with the area code”, so abviously the system thought it was a number in the 905 or 289 area code (my location, the 289-905 area-code overlay zone) with exchange code 932.
Evidently the system is smart enough to distinguish the destination numbers of text messages from the destination numbers of voice calls. And why not? Text messages travel along different paths than voice calls…
I have occasionally seen 5 digit numbers on my cellphone caller-id for incoming calls. Invariably they were telemarketers (even though they were calling my cell AND I’m on the DNC list, but that’s a topic for the Pit).
What’s the deal with this? Can these “special” numbers make outgoing calls?
No, that’s the telemarketers illegally ‘spoofing’ their outgoing caller-ID info. Apparently you can program pretty much anything you want into a PBX’s outgoing caller ID. I’ve seen real numbers, short numbers like “2809”, and nonexistent numbers like “000-000-0000”.
There is a legitimate reason for this: if you have a business with fifty outgoing lines, it’s better for the recipient of the call to get the main business number of the firm calling, rather than whichever line number the outbound caller happened to use. That w2ay, the recipient can call back to a real number and get service. Outgoing lines sometimes can’t even accept incoming calls.
But the scummier end of the telemarketing industry uses this capability to announce themselves with fake numbers instead.
Are you saying there is a non-scummy part of the telemarketing industry?
This is what happens. I worked at one of the Finnish mobile operators one summer, and a lot of the contracts that I had to process involved different mobile entertainment companies which had to enter into a separate agreement with every operator they wished to support their “buy a Coke from the vending machine with your cell phone” or “Free ring tones and background images” service. When these companies advertise, they have to provide a list of the operators which support their service. Sometimes you’ll get a service which isn’t supported by one; before, you used to sometimes have services where clients of different operators had to text different numbers.
The short codes you list appear to work only for Fido users.
I’m not surprised. I thought the WEATH one was supported by all carriers, though.