. as a percentage of net sales in 2006 as compared to 2005 , gross margin , sg&a expenses , r&d expenditures and operating margin all decreased . in 2006 , net sales to the segment 2019s top five customers , which included sprint nextel , comcast corporation , verizon , kddi and china mobile , represented 45% ( 45 % ) of the segment 2019s total net sales . the segment 2019s backlog was $ 3.2 billion at december 31 , 2006 , compared to $ 2.4 billion at december 31 , 2005