Why did Nebraska end up with the short end of the stick for so long? The answer lies deep in some silly rules imposed by the Bell System, combined with an odd bit of Cold War surplus.
In the United States, before the deregulation of telephone services, nearly the entire country was under the stranglehold of the Bell System — "Ma Bell", as it was often called. The phone company (and when people said the phone company, they meant the phone company) had a lot of seemingly random and mostly self-serving provisos. To give you an idea, customers back then weren't even allowed to buy a telephone — technically, you could only borrow it from the phone company, and the Supreme Court had to step in to tell Ma Bell to knock it off. Several of those rules applied to the 800 system, the most relevant being that (a) the country was divided into "bands", and calls were more expensive the more bands they crossed, and (b) you couldn't use the same 800 number for calls within a state and for calls between states. Why? We don't know. But that was the rule.
Mail-order companies who wanted to take advantage of the new 800 service were looking for places to set up shop. But this was easier said than done, because the Bell System had no incentive to build any more infrastructure than was necessary in any given region. But there was one big exception — Omaha, Nebraska. Just south of the city was Offutt Air Force Base, which hosted the Strategic Air Command, the Air Force command tasked with managing the entire Air Force's nuclear weapons arsenal. They asked for insane amounts of incoming phone lines, as insurance in case of an attack. And the Bell System had obliged.note This left Nebraska with a ton of phone lines, most of which went unused 365 days a year.
The 800 services saw an opportunity, especially given that Nebraska was right in the middle of the country, which meant they could easily reach the entire contiguous U.S. without getting the Bell System's most expensive rates. They asked Northwestern Bell nicely if they could make use of the dormant phone lines. And they said yes, but the 800 services would be cut off if the Soviet Union attacked (well duh), and they had to follow all the rules. But one of those rules was that you couldn't use the same 800 number within the state and outside the state. So, to avoid confusing potential customers with two 800 numbers, 800 services just gave the interstate number and told Nebraskans that they were out of luck. (Some may have made a separate ad for Nebraskans with a separate number, but most people wouldn't have seen it.)
Eventually, Omaha became such a haven for these 800 services that they exhausted the SAC's extra phone lines, and Northwestern Bell built more and more phone lines, to the point that the call centers' lines dwarfed those originally set aside for the SAC. But the rules about 800 numbers didn't change until 1993, by which time SAC had been disbanded into the current STRATCOM. And Now You Know.
Nowadays, you might still see "Offer void in [such and such place]", but it won't generally be Nebraska. In some cases, this is due to local advertising rules that prohibit certain kinds of ads. Tennessee, for instance, has heavy restrictions on advertising from out of state (because there's no state income or interest taxes, so shopping local is crucial), especially regarding gambling. In other cases, it's just due to the added expense of shipping to a faraway place; offers may be void in Alaska and Hawaii, or U.S. territories (other than Washington, D.C.). The same thing happens outside the United States; in Canada, Quebec is often excluded because of its gambling laws and French language requirements, and in the United Kingdom, there might be exceptions for Northern Ireland, the Channel Islands, and other places outside the British mainland.
