Well! You followed this link so now you're gonna get my simplified description of the international allocation of radio call-signs.
Amateur Radio call-signs, or those issued for other radio services, are not assigned in a vacuum. The International Telecommunications Union (ITU) is the governing organization for all electronic communication regulations worldwide. ITU regulations are developed at various worldwide conferences where any signatory nation may propose changes to any regulations within the scope of the conference. The ITU pre-dates the United Nations and it has no power of itself to enforce the regulations decided at its conferences. The enforcement of regulations is on the shoulders of each nation that agrees to be bound by ITU regulations. Yes, there are rogue nations that don't participate and those that agree to be bound and yet do their own thing, causing headaches for the rest of the world.
The Federal Communications Commission is the agency charged by Congress to enforce the ITU regulations adopted by the United States and tailor those generally broad regulations into more specific rules suitable for everyday use. The FCC is also responsible for licensing individuals and entities that qualify for the various radio services and granting them licenses in those services. When issuing a license for a specific radio service, the FCC uses one of three letters of the alphabet assigned exclusively for use by the USA (there is actually a fourth, more on that later). This letter is known as a "prefix" and is what sets USA call-signs apart from those issued by other nations. Since there are a bewildering number of radio services administered by the FCC, a different type of letter and letter/number combination exists for each service. Some examples are:
WKRP ... Broadcast station
KBPA5404 ... Land Mobile radio service
KAØRNY ... Amateur Radio Service
KA2XXX ... Experimental (Note similar format to Amateur Radio)
Since I am most familiar with Amateur Radio Service calls, I will concentrate on those. Looking at my previous call, we can break it down to three parts: prefix, call area, and suffix. The prefix is KA, I was licensed in the tenth call district -- Ø, and my suffix is RNY, a sequentially assigned combination of letters generated by the FCC's computer. In other words, the prefix and call area of my call were predetermined by virtue of living in the USA in the state of Kansas and the suffix was the "luck of the draw." The entire call was actually determined by one other detail, the class of license I applied for in October, 1983, in this case Novice.
As I said earlier, there are three letters assigned exclusively to the United States. Those letters are K, N, and W. K and W are familiar to nearly every US citizen as the FCC has issued calls using both letters to radio and television broadcast stations. N is more obscure, its use being limited to Amateur Radio and a few other services. A fourth letter, A, can be used by the US in combination with a second letter. This group runs from AA to AL and any call heard with a prefix of AM to AZ is from one of several other countries. So, here are some legal U.S. amateur calls:
KAØRNY ... "two by three" format, Group D
W5DRT ... "one by three" format, Group C
KM5DH ... "two by two" format, Group B
NØNB ... "one by two" format, Group A
NJ5S ... "two by one" format, Group A
AAØMV ... "two by two" format, Group A
KØV ... "one by one" format, Special Event
These are the FCC designated formats and groups for calls. In general, shorter calls are assigned to higher class operators, if the operator desires it as operators may keep a call they are currently assigned even when they upgrade their operator privileges. The groups are assigned as such:
Group A: available only to Amateur Extra Class licensees.
Group B: available to Advanced or Extra Class licensees.
Group C: available to Technician, General, Advanced, and Extra class licensees.
Group D: available to Novice and higher licensees.
Since the higher license classes can get shorter calls, it stands to reason that those calls are the most limited in availability. So, the FCC devised a cascade system where if a certain group of calls in a given call district (Ø to 9) is exhausted by the computer, it will begin to assign calls from the next lower group. In fact Group C calls ran out a few years ago in all call districts after which the FCC assigned Group D calls to new Technician and General class licensees. This occurred because the FCC only assigned calls beginning with N from the Group C block and would not issue un-assigned calls beginning with K or W in Group C. The vanity call system has re-activated many of those dormant calls, more on that later, as well.
When the FCC started assigning the calls in the block mine was drawn from, they began with KAØAAA, the next was KAØAAB and so on. Somewhere around mid-1986 KAØZZZ was assigned and the computer assigned KBØAAA next. Notice the sequence. Suffixes are assigned from AAA to ZZZ and then the second letter of the prefix is incremented. In the case of Group C calls, when NØZZZ was reached, the computer started assigning somewhere in the KBØxxx block. For Group B, the suffixes run from AA to ZZ and then the second prefix letter increments. For Group A there are at least three scenarios. I'm sure you'll be able to guess the pattern of 1X2 and 2X1 calls, yes, it would go like this: KØAA to KØZZ, NØAA to NØZZ, and finally WØAA to WØZZ. The only trouble is the FCC hasn't assigned 1x2 calls sequentially for many years. Instead, when the FCC went to this sequential assignment system in early 1978 they opted to assigning 2X1 calls to those Amateur Extra Class licensees that applied for them. So the order went like this (grossly over simplified!) including the AA to AL prefix: AAØA to ALØZ, KAØA to KZØZ, then NAØA to NZØZ, and finally WAØA to WZØZ. When WZØZ was assigned the computer skipped to...? Well, it didn't go to Group B, instead the FCC set up a special Group A block that used Group B (2X2) format and is being assigned like this: AAØAA to ALØZZ. This is a detail that confuses some radio amateurs who mistake these Extra calls for Advanced calls.
The FCC has reserved several prefixes of all call districts for areas outside the "lower 48." These include: AH, KH, NH, and WH, for Hawaii and certain Pacific islands; AL, KL, NL, and WL for Alaska; KP, NP, and WP for Puerto Rico; and KV has been used for the Virgin Islands. These prefixes are not routinely assigned to hams in the Continental U.S., however, you will find active hams in the Continental U.S. sporting these location dependent prefixes. About the only way to get one of those prefixes is to have a mailing address in one of the locations. There are other prefix combinations reserved for other uses and if you're interested poke around the FCC's web site and you'll probably find out what they are!
The Special Event category deserves a closer inspection. These calls are not assigned by the FCC nor are they permanently assigned to individual licensees or clubs. They are, however, valid U.S. calls and you will find them in use as the calls of a special event station on the air celebrating some notable occasion. Special event calls are assigned for a limited time by an (independent of the FCC) call-sign coordinator and the assignee must use their permanently assigned call once per hour when using a special event call. For more details consult Part 97.
Beginning in mid 1996, the FCC inaugurated a new way of assigning calls, namely allowing radio amateurs to pick a call themselves! This represented a radical new direction in call assignment as hams had never really been able to ask for their call of choice except for a period in the '70s when Extra Class operators could pick a 1X2 call for a limited time. The Vanity Call System as it is known has been opened in several timed "gates," the first allowed current licensees, regardless of license class, the opportunity to reclaim any previously held call. The next gate allowed current licensees to claim calls assigned to deceased relatives. Gate 2, as the third gate was called, allowed any Extra Class operator to request any unassigned with up to 25 choices in order of preference allowed on the application form. Gate 3 allowed Advanced Class operators the same opportunity. Currently all gates have opened extending the opportunity to General, Technician Plus, Technician, and Novice Class operators. Of course, only currently unassigned calls can be issued and there is a two year period when a call is not assignable except under special circumstances when a license lapses its term.
As with the sequentially assigned system, operators will be limited by license class on what calls they can request. Extras, of course, may request a call from any of the four groups. Advanced operators may pick from Group B and lower. General, Tech Plus and Technicians, presumably from Group C and lower and Novices from Group D. An added twist to the system allows any operator in the contiguous 48 states to request an available call that would otherwise be outside his home call district. For example, someone in Kansas can, and has, request a call with a 1 as the digit even though Kansas is in the Ø/tenth call district. Finally, operators in the contiguous 48 states may not request a call that has a prefix reserved for Alaska, Hawaii, and the territorial possessions. To get one of those calls, an operator must apply with a mailing address in one of the qualifying areas. I suppose an operator in one of those areas could request a call assigned to the contiguous 48, but why would they want to?
Like a lot of other hams I decided to take part in the "Vanity Insanity" and request a call of my choice. Looking at the available calls revealed NØNB to be available. Not only are the last two letters my initials, it's not a bad CW (Morse Code) call and it sounds good on voice. My application was processed and NØNB assigned on December 15, 1998. KAØRNY has now been marked as inactive in the FCC's database and is not available for re-assignment for two years. As I understand it, I am the only licensee able to reclaim it in that two year period, but would have to give up NØNB to do so. Have I missed the old call? Yes I did for the first few months. After being very active on the radio with KAØRNY for nearly 15 years, the call assumed an alter identity and it took some time to adapt to NØNB. There were too many times when I started to identify and I said "K" before realizing I should have said "N..." Now, nearly a year after getting NØNB, I am pleased with my selection. It is my new alter-ego and has been fun to use on Field Day and other operating events. I am glad the FCC was finally able to establish a system that allows hams to choose call letters based on their personal criteria and not just "luck of the draw."
As you now know, considerable detail has been given by the FCC to the system of Amateur Radio call-sign assignments. Hams hold calls nearly more dear than their given names! There may be thousands of John Smiths in the world, but only one WB2YUZ. The thought given to international and domestic call-sign assignments sees to that. So, now you can believe me when I say I am truly "one in nearly five billion!"
taken from http://www.n0nb.us/ham-linux/ham/callsigns.html
CW ataupun Continuous Wave SSB ataupun Single Side Band CW SSB