Explain xkcd: It's 'cause you're dumb.
Title text: There's also a +1 sometimes, which is there to keep everyone on their toes. In the future, people who got to pick cool numbers by signing up for Google Voice early will be revered as wizards.
This comic references the pattern for US telephone numbers, which are ten digits in length. Unlike in other countries, there is no quick way to determine whether that number is for a land-line or mobile customer. In either case, the first three digits are referred to as the "area code", a term dating back to before the proliferation of mobile phones, when specific codes were assigned to geographic regions. The next three digits had some rules based on the telephone exchange but as Randall says, those and the final four numbers are essentially meaningless.
In the early days of the mobile era, the geography-based numbering still applied to new mobile lines, so mobile phones would have the same area code as owners' home numbers. Late in 2003, US telephone service providers were required to support "number portability", meaning that customers could theoretically take their mobile phone number with them to a new provider, even when moving to a distant new location. In the early days this wasn't always very easy to do, but became commonplace within a couple years. Since most users opt to keep their numbers constant whenever possible, numbers generally stopped changing after about 2005, instead of shifting when people moved like they were forced to in previous years. Therefore, examination of a given phone number will likely tell you where its owner was living at that time, since their number would not have changed after 2005 due to the portability law.
Google Voice is an alternate voice over IP service. Upon signing up, users can choose any available new 10-digit number without regard to geographic area. Among other things, this allows the earlier users to choose "cool numbers" if desired, such as ones that correspond to phonewords or have a pleasing pattern. In the past, this "vanity numbering" was typically only available to businesses via toll-free numbers. Some mobile service providers began allowing similar customization after the portability law, but often still restricted new numbers by area code, keeping the availability of "cool numbers" low until Google Voice launched.
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- [10 boxes for 10 digits of a U.S. phone number. The first three are grouped by parentheses. A hyphen separates the second set of three and the last four.]
- [Label titled "Your seven random digits" pointing at seven empty boxes.]
- [Label titled "Where you lived in 2005" pointing at three empty boxes preceding the seven.]
- Structure of a US cell phone number.
In the explanation: "The next three digits are the exchange number (the middle digit being always 2 or higher)". That cannot be true. After my area code, my exchange number is 504...the middle digit being a zero i.e. <2. Where did you get the information that the middle exchange number has to be a 2 or higher? That source should be corrected as well See This Link.--Dangerkeith3000 (talk) 17:13, 5 November 2012 (UTC)
- The limitation being discussed existed only until the 1990s. See .CityZen (talk) 19:28, 6 November 2012 (UTC)
- I reordered some paragraphss so that hopefully it makes more sense: the first paragraph sets up the history; the third paragraph reflects current reality; the second is the transition. -- IronyChef (talk) 05:16, 7 November 2012 (UTC)
- I see. The "Prior to the proliferation of cell/mobile/handy phones..." stated in the first paragraph sets it up as historical numbering (i.e. rules prior to 1990) and not the current rules. It has been reordered very well to make more sense (at least to me!).
I guess this has something to do with keeping your phone number even when switching providers? We got a law in Norway around that time, which says you're able to keep your phone number while switching. Only difference is that here you can only tell, from the first two of eight digits, which provider you had in 2005 (or whenever it took effect). --Buggz (talk) 08:31, 2 November 2012 (UTC)
- It probably does. There is no mention of 2005 in North American Numbering Plan wikipedia article ... seems it's the part needing explanation the most. -- Hkmaly (talk) 08:38, 2 November 2012 (UTC)
- According to wikipedia, mobile number portability was implemented in the USA in 2003.11.24. The comic would make sense with 2003, but why 2005? Maybe it only caught on enough in 2005: http://www.pyramidresearch.com/pa_may26_mnp.htm
- One reason for switching to a new "local" number would be so that those who have land lines aren't making "long-distance" phone calls to your cell phone. My brother just recently moved back from the east coast and is keeping his same cell phone number, which doesn't affect my other siblings and myself because we only use cell phones (which only count the number of minutes used). But my mom still uses land lines most of the time and so she's being billed for a long-distance call whenever she calls him, even though he lives about a mile away from her. But since most people are ditching the land lines, I think it'll be a moot point in about 5-10 years. --Joehammer79 (talk) 13:45, 2 November 2012 (UTC)
It has to do with cell phones versus land lines. Back in the day (before the early 2000s), many people still had a land line as their primary or only phone. Your phone number's area code would be based on the area in which you lived. If you moved to a new area, you would get a new phone number, and if you moved out of the previous area code, a new area code. But with a cell phone, when you moved you kept the same number, including the area code. This was especially true after the 2003 law made it so you could keep the same number even if you switch your provider. The year 2005 has to do with when many people made their cell phone their primary or only phone. As this USA TODAYarticle mentions, in 2003 18% of Americans with cell phones considered their cell phone their primary phone. Given the rapid growth of the industry, it is possible that 2005 is when more than half of cell phone owners in America considered their cell phone their primary phone.
- The details differ, of course ("your mileage may vary"). There are so many possible reasons why this occurs. My parent's cell phones (612) don't match their home land-line (763) due to area code splits -- they didn't move or cause the disconnect themselves. As for me, my first cell phone matched theirs, but in 2005 I moved to Michigan (586 area), creating a disconnect. Then to make things worse, early next year (2006) I got a second line (and new phone) on my new girlfriend's account, and she lived on the other side of the city (734). We married and moved near where I was living & working, but both still have "734" cell phones for family purposes. So Randall's "living" can also be "dating / where significant other is living". --BigMal27 / 126.96.36.199 15:54, 2 November 2012 (UTC)
For anyone from outside the US, the key fact here is that in the US, your mobile phone has an area code the same as a landline. I used to live in the US, and it blew my mind to learn that mobile phones had area codes there. I was like, but.... Huh? That's like saying your car has a postal address.Carlisle (talk) 15:06, 2 November 2012 (UTC)
- In the US, our cars kind of do have a postal address -- the state they are titled & registered in, the same state emblazoned on the license plate in the back (and sometimes the front also). However, the states don't like it when you operate an "out-of-state" car in their territory for too long. Specifically, you are using public roads that you are not paying for. Then, when you transfer title and are assigned a new plate, you get a new letter/number combination. License plates -- and specifically the random ID (or "vanity plate" custom ID) they hold -- are not portable between states. --BigMal27 / 188.8.131.52 15:47, 2 November 2012 (UTC)
- In the past, in Italy you had to do the same when you moved from one province to another. Now, if you move, you pay car taxes to a different province, but your license plate stays the same. At the time, the province code was part of the license number, now it isn't anymore. If you have an old plate with a province code, you keep it even if you move.
- If you have an out-of-country car, and move to Italy for more than a year, then you have to get Italian license plates.
- --184.108.40.206 17:51, 2 November 2012 (UTC)
- In Poland the license plate starts with three letters encoding the county (voivodeship and powiat) --JakubNarebski (talk) 10:28, 3 November 2012 (UTC)
- In the UK the first two letters on a car's plate are for where it was registered, but after that they may as well be meaningless, you do see more S plates in Scotland, M plates in Manchester etc. but the letters don't always even indicate the car was bought as new in that place, I take photos for car dealers and you often see new cars for sale with plates from other parts of the country. Still, actually being able to post to a car would be funny.
- On the subject of postal addresses, I had an Irish friend at uni, and when we were exchanging addresses to write to each other at the end of first year he gave his address as (not his real name, obviously) Sean Murphy, Kilbeggan, Ireland. We all laughed but he said, the postman knows who everyone is so they don't need street names and numbers, we asked what if they got a new postman, and he said 'that wouldn't happen'.Carlisle (talk) 23:10, 4 November 2012 (UTC)
I'm 34 and live in the USA and it still took me a while to understand this. The 2005 date is because even though the portability law was passed in 2003, it was still difficult to do and not very common to keep you number until 2005.
 Handi phones
"cell/mobile/handi phones" ... Who uses "handi phones"? Would be really interesting :) --Kronf (talk) 02:18, 3 November 2012 (UTC)
- A German friend tells me that that is the term of art for what US folks call "cellular" phones: "Ruf mich am Handi an," (in my broken German: "call me on my handi/cellphone") Given that we've got an international audience, it seemed appropriate to use. -- IronyChef (talk) 02:31, 3 November 2012 (UTC)
- Ah ok. And you had me thinking that someone in the English speaking world was using our German term ;) --Kronf (talk) 02:43, 3 November 2012 (UTC)
- But we write it "Handy" ("Handi" (with a german "i") is how you speak it – the letter "y" can be a "i"- or a "ü"-sound in German). --DaB. (talk) 16:32, 3 November 2012 (UTC)
- I stand corrected, then... -- IronyChef (talk) 04:36, 4 November 2012 (UTC)
In my overhaul I've tried to change all references to the simple "mobile phone". This is a literal definition and as such shouldn't fall victim to confusion about regional terminology like "cell". Let me know if you're aware of an audience that would not understand "mobile", or just add the appropriate clarification yourself. - jerodast (talk) 17:37, 22 December 2012 (UTC)
 Bloated explanation
There is a lot of information about the structure of US phone numbers here, and while general information is good to set up the joke, the specifics can be left to the wikipedia article. Specifically, all the talk of how exchanges are numbered and long distance charges is utterly irrelevant to the strip, and the information about choosing custom numbers is relevant only to the title text (and takes about one line to explain). The meat of the joke is that area codes used to be location-based but rapidly became more flexible around 2005, resulting in that rather arbitrary meaning today, yet this is mentioned almost casually in just one sentence near the end. I will trim and reorder the article so that it's more relevant to the comic shortly, unless there are objections. - jerodast (talk) 11:01, December 3, 2012
- Quite a few explanations are like that. People add things that seem relevant to them, but don't really help explain the comic. If you look at most of the explanations past the 1050 mark, quite a few of them aren't perfect. If you want to tighten them up, by all means do so. Davidy22[talk] 00:39, 4 December 2012 (UTC)
 Additional Info on Phone Numbering Systems
I trimmed a lot of unnecessary information from the explanation, because it had nothing to do with explaining the joke of the comic. For those parties looking for more information on phone numbering plans, here is what I removed:
- The middle digit of the area code was originally always 0 or 1 to allow mechanical dialing circuits to identify the sequence as an area code or not.
- The next three digits are the exchange number (the middle digit being always 2 or higher), and the final four digits are typically random.
- Business customers frequently could pay a premium for a specific number (if available), either to spell a brief slogan, or for easy memorization.
The prevalence of digitally controlled dialing allowed the restrictions on digits in area codes and exchanges to be relaxed, suddenly making many new area codes and exchanges available. According to the North American Numbering Plan, currently:
- The first 3 digits (Area Code) can be [2-9][0-9][0-9],
- the next 3 digits (Exchange) can be [2-9][0-9][0-9], and
- the final 4 digits (Subscriber Number) can be [0-9][0-9][0-9][0-9].
There are some rules
for area code exceptions or reserved numbers though. Specifically, X11 codes are not valid as area codes (e.g. 411, 911, etc...) and Xyy (repeated last 2 digits) codes are reserved for special use area codes (e.g. toll-free/freephone 800, 888, etc..). - jerodast
) 17:44, 22 December 2012 (UTC)