Of course, for cell phone service companies there's no point in putting up cell towers in areas where there are likely to be few users. The map, thus, shows that coverage is best in the most prosperous and populated areas of the world. The eastern half of the US, for example, appears to be well covered, although there are many gaps (where there is only a weak or no signal), even in places like the New York metropolitan area. Further west, where there are fewer people (in the mountains and deserts of Colorado, Utah, Nevada, for example) coverage becomes more patchy, once again returning to east coast levels along the California coastal strip.
How do people travelling through those areas, or those in non-covered areas (such as workers on oil-rigs or other remote installations), or in areas near borders, communicate? The "easy" – and expensive – answer is via satellite phones.
At one, two or three dollars a minute, communicating via satellite is very expensive, which is why many travelers and workers in areas not covered by cell service just do without.
But it turns out that not all satellites – or satellite phone calls – are equal. A far cheaper satellite alternative can provide phone calls and text messages for mere pennies, using High-Throughput Satellites (HTS) that are located on a geostationary orbit above the equator.
HTS/GEO satellites were initially launched into space to address the immense demand for TV broadcast and internet access. The idea of using HTS satellites for voice is somewhat novel – most satellite phone calls are currently made using LEO (low earth orbit) satellite networks, which have much lower capacity than HTS. Although LEO satellites have been in the skies for decades, they have remained out of reach for all except those who work for organizations with deep pockets (government, oil companies, etc.) and have no other communications options.