2006 saw Mt. Everest (yes, the world's highest mountain) experience a total of 3,050 officially recorded ascents, 2,062 climbers, and 203 unfortunate fatalities (source article on Wikipedia).

Now, thanks to China Mobile and Huawei Technologies, there'll be at least 1 GSM base station on this climber's challenge:

china mobile has hired Huawei Technologies to install a GSM Base Station on Mt. Everest. The base station will be positioned at 6,500 meters and can run on solar power. The base will be positioned so communication can be made between base camps and the main rout to Everest's summit. It will be able to communicate with satellites, so a call from the mountain can reach almost anywhere on the globe.

Some side notes: Huawei is well-known in my country as the supplier of HSDPA peripherals, including USB and PCI HSDPA equipment designed to provide laptops with mobile connectivity via next-generation GSM-based cellular networks. This post also shows that GSM is definitely more widespread than competing communication formats.