In a letter by 25 investment funds...fund managers warned companies ranging from Yahoo to Cisco of the risks in "collaborating to suppress freedom of opinion and expression"..."We take this issue very seriously," Yahoo spokeswoman Mary Osako said..."While foreign-based companies must adhere to local laws in all the countries where they operate, we understand that there are unique and inherent challenges to doing business in China," the Yahoo spokeswoman added...Other companies singled out...included Google Inc. and Microsoft Corp...No one from Google, Microsoft or Cisco Systems was immediately available to comment. [also refers to Nortel, Fortinet, Secure Computing]