PART I Domestic fixed communications  Mobile communications  Internet  International fixed communications  Others  Income from operations and Operating Margin  77 The following table sets forth certain information regarding our operating income by business segment for  the periods indicated.  As a result of the foregoing, our income from operations increased by 1.7% from NT$56.4 billion in 2009  to NT$57.4 billion (US$2.0 billion) in 2010. Our operating margin decreased from 28.5% in 2009 to 28.3% in  2010.  The costs and expenses from our other business increased by 31.7% from NT$4.6 billion in 2009 to NT$6.1  billion (US$0.2 billion) in 2010. The increase was primarily due to the consolidation of our subsidiaries.  Our international fixed communications costs and expenses increased by 1.9% from NT$14.2 billion in  2009 to NT$14.5 billion (US$0.5 billion) in 2010. The increase was primarily due to an increase of NT$0.1  billion (US$4.1 million) in equipment rental expense and an increase of NT$0.1 billion (US$3.4 million) in  corporate solution services and ICT costs.  Our internet operating costs and expenses increased by 4.5% from NT$15.1 billion in 2009 to NT$15.8  billion (US$0.5 billion) in 2010. This increase was primarily due to a NT$0.4 billion (US$14.4 million) increase  in leased line expenses.  Our mobile communications operating costs and expenses increased by 6.6% from NT$58.3 billion in 2009  to NT$62.1 billion (US$2.1 billion) in 2010. This increase was primarily due to an increase of NT$2.4 billion  (US$ 81.9 million) in cost of handsets sold, and an NT$1.0 billion (US$33.6 million) increase in leased line and  internet access expenses.  Our domestic fixed communications costs and expenses decreased by 0.9% from NT$67.6 billion in 2009  to NT$67.0 billion (US$2.3 billion) in 2010, primarily due to a NT$2.1 billion (US$69.9 million) decrease  in depreciation and amortization expenses reflecting a slowdown in capital expenditures, partially offset by a  NT$0.9 billion (US$30.5 million) increase in corporate solution services and ICT costs and a NT$0.8 billion  (US$29.5 million) increase in bonus.  Domestic  Fixed  Communications Mobile  Communications Internet  International  Fixed  Communications  Others Adjustment Total (in billions of NT$) For the year ended December 31, 2010 Revenues from external customers 70.7  89.0  24.5  15.5  2.7  — 202.4  Intersegment service revenues 14.7  2.1  1.1  1.7  0.7  (20.3 ) — Interest income — — — — 0.5  — 0.5  Other income 0.3  0.1  0.3  (0.2 )