On the ground: GSM world coverage
I found this nice little map (PDF link) a while back from GSM Association, which shows GSM coverage on the entire planet. It's very nice looking, and really goes to show that the world runs on GSM (or 76.2% of the world to be precise). We can clearly see which areas are covered, and as far as developed countries go, it's almost everywhere.
The map shows numbers as well, like over 2 billion GSM users, 38% of them being in Asia / Pacific. It also shows how fast people are getting phones. One thing that would be nice is if they showed frequencies. Right now there are 4 popular frequencies (850, 900, 1800, 1900 MHz), with a couple more being used in odd places like 450 MHz. Most phones sold are either dual-band or tri-band, but at least if you get a quad-band GSM phone, you can clearly see why they call it a "World" phone.