My colleague Jonathan recently surprised me by explaining that he doesn't have a mobile phone as a matter of principle, because the trade in coltan - an essential mineral for manufacturing mobile phones - is propping up the rebels in the DRC.
While most of the world's coltan comes from legitimate mining in Australia, Brazil and Canada, a worrying amount passes through warring hands,and there is little way of knowing which is which. This report from 2001 explains how money and wars are made through our calls:
Given the substantial increase in the price of coltan between late 1999 and late 2000, a period during which the world supply was decreasing while the demand was increasing, a kilo of coltan of average grade was estimated at $200. According to the estimates of professionals, the Rwandan army through Rwanda Metals was exporting at least 100 tons per month. The Panel estimates that the Rwandan army could have made $20 million per month, simply by selling the coltan that, on average, intermediaries buy from the small dealers at about $10 per kg. According to experts and dealers, at the highest estimates of all related costs (purchase and transport of the minerals), RPA must have made at least $250 million over a period of 18 months. This is substantial enough to finance the war. Here lies the vicious circle of the war. Coltan has permitted the Rwandan army to sustain its presence in the Democratic Republic of the Congo. The army has provided protection and security to the individuals and companies extracting the mineral. These have made money which is shared with the army, which in turn continues to provide the enabling environment to continue the exploitation.
And more information on guns, money and cells phones is avaliable if this has got you worried.