The answer is 2.4 GHz to _____GHz. The official range of radio waves in the United States is between 3180-3200 MHz and 2500-2690 MHz, but they can also be found in a much more conflicting portion of the spectrum: 7.35-7.48 GHz and 2.4-3 GHz (2.4 GHz is part of the digital TV spectrum, but it’s not well understood yet.) The spectrum in question is “part of the foundation on which wireless communication and data broadcasting will be built in the next century,” according to a 1998 FCC deregulation plan.
The spectrum between them has a long and interesting history. The portion 7.35-7.48 GHz was originally intended to be used by government for radar systems, but this was abandoned due to delays by both World War II and the Cold War. Spectrum management was in the hands of the Federal Communications Commission since the Department of Defense had no position on spectrum use. In 1953, in response to requests from private companies (who wanted to build radar systems), the FCC began auctioning off spectrum in this band, but the frequency range that became available wasn’t accepted by any interest group. In 1970, a new effort was started by General Electric and other companies to create a radio system for citywide metropolitan area applications. But once again it failed. By 1978, equipment producing radiation at 7.35 GHz was being sold in Japan. The first system in the United States using this frequency was put in place by a private company in 1984.
In 1985, equipment producing radiation at 7.35 GHz was also being sold in the United States. By February 7, 1987, all frequencies between 7.35 and 7.48 GHz were allocated to radio astronomy use on a secondary basis (FCC 87-54). This allocation is superseded by the new Table of Frequency Allocations effective March 18, 1997 (Federal Register February 15, 1997) which lists them as indefinitely available for shared Federal/non-Federal use as ground support systems (GS).
Also, it is superseded by the FCC Report and Order: “Development of the 3 GHz Band,” released April 30, 1998, which indicated that this portion of spectrum was reallocated for Federal use and was removed from non-Federal status. It’s important to note that while they were previously being used by private companies, this allocation actually means nothing in terms of private ownership. In fact, no one owns this part of spectrum–it doesn’t belong to anyone (EDIT: as explained in the comments below). What it means is that it can be used in any way by anyone (within certain regulations)–not owned by anyone per se.
The 2.4 GHz range has a similar history. It was originally established for educational use, but the FCC was wary of interference with television broadcast and other communications bands on this spectrum. A big fight ensued between the television, microwave relay, and amateur radio communities. In 1952, the FCC first allocated part of this band for wireless microphone application under the low-level power provisions. The first commercial standard for this service appeared in 1960 (R-53). Wireless microphones in the United States operate between 2.3 GHz and 2.7 GHz under Part 15 (the same frequency range is used for cordless telephones). The 2.4 GHz frequencies were allocated to radio astronomy use on a secondary basis (FCC 87-54) by the FCC in 1985 and is superseded by the FCC Report and Order: “Development of the 3 GHz Band” released April 30, 1998 which indicated that this portion of spectrum was reallocated for Federal use and was removed from non-Federal status.
The 2.4-3 GHz band has been known as the “magic band” since it’s higher than most local licensed services, but not quite high enough for long distance communications. It’s also a great frequency range for spread spectrum communications (like Bluetooth) because it’s in between many other ranges used for other communications devices–making interference much less likely. As an example, the FCC requires a guard band of 5 MHz or more with other industrial, scientific and medical (ISM) applications at 3.1 GHz. The FCC will regulate usage of this spectrum to make sure the airwaves are free from interference with other communications services (such as telephony) and that it is used for a specific purpose.
Most of the consumer electronics devices on the market use 2.4 GHz today–the most popular being Wi-Fi devices as they are just cheap and easy to use. There are also many wireless microphone systems in this band, along with home alarms and garage doors that open when people come close enough to them using magnetic switches.