This week, Comcast announced  it would begin the first official commercial rollout of 4G wireless broadband in the U.S. in Portland, Oregon, after using Baltimore and Atlanta as test markets. The company plans to bundle the WiMAX service, which is about twice as fast as 3G network speeds, with its "Triple Play" cable and Internet offering as a wireless Internet service for laptop users.
WiMAX is the first inkling of what will be a new generation of consumer-oriented services set to roll out before the end of the decade, some of which will take advantage of newly-licensed radio spectrum. Since mandating that antenna TV go digital, the FCC has auctioned off various slices of the radio pie, which is managed by the NTIA , to the highest bidder; big winners  in the 2008 auctions were Verizon and AT&T, who plan to build their own 4G networks, dubbed LTE.
And yet, vast swaths of spectrum go largely unused on a day-to-day basis, for things like aeronautical and emergency communications. Some technologists  are arguing that the system be upgraded to allow spectrum sharing, which begs the question: just how complex is this thing, anyway? If you've got about 10 hours to kill, check out the NTIA's spine-tingling "Allotments, Allocations and Plans " report. If not, it works like this: the world is divided up into three radio regions.
In the United States, spectrum is reserved according to this satanically complex map. Here is one tiny slice of it.
And here's the thing in its entirety. Click through for the full size and enjoy; it's about the size of your bedroom wall.