Coltan (columbite-tantalite) is used in the production of pinhead capacitors. These aren't just in cell phones, but are also in lots of other high tech toys and tools from palm pilots to video games. As demand has increased, the price per kg of coltan has risen by an order of magnitude in the last decade. Most of the world's known reserves of coltan are in the Democratic Republic of the Congo (DRC), with another fair-sized chunk in Australia. Currently, most production comes from Australia, although production in the DRC is ramping up as demand increases.

What seems to be happening in the DRC is that loggers are clearing roads into the forest, which opens up access to miners. The gorillas, amongst many other species, are being poached for "bush meat". The biggest problem in the region is ongoing political instability and civil war. Local militias get a kick-back for allowing logging, mining, and poaching in the areas that they control. These funds are used to further finance the war.

The United Nations has condemned the carnage, and manufacturers of high tech goods are being urged to demand guarantees that the coltan supplied to them was obtained legally.

For background reading start with these two sites:

http://www.ecoisp.com/species20.asp
http://gorillaaid.org/news/cellular_death.htm