A top cancer expert warned on Thursday that it will probably take a decade before scientists know for certain whether today's GSM mobile phones pose a health risk. Another scientist insisted that more research is needed into the issue. The mobile phone industry has consistently tried to reassure consumers by insisting there is no evidence that mobile phones pose a health risk. But Professor Lennart Hardwell told the Mobile Telephones and Health conference in London that we are still a long way from knowing for sure what the true dangers of mobile phone use are. He believes it will take ten years for studies into the issue to be completed -- by which time GSM will have been superseded by third-generation (3G) phone networks. GSM phones transmit using the 900MHz, 1800MHz -- and in America the 1900MHz -- frequencies. Scientists have proven that radio waves of these frequencies can generate significant electric fields within human cells. 3G networks, which will offer much faster data transfer rates than 3G, are expected to be operational by 2004. In the UK they will operate between 1920MHz and 1980MHz, and between 2110MHz and 2170MHz. Little research has been carried out yet into health dangers of 3G. A second scientist, Professor Lawrie Challis, told the conference that more human volunteers were needed if scientists were to accurately assess the risks of exposure to mobile phone emissions. Professor Challis, who took part in the government-backed Stewart Inquiry into the risks of mobile phone use, said that researchers still have a lot to learn about the impact of mobile phone emissions on human brain functions, according to the Electronics Times. The Stewart Inquiry, which issued its report in May 2000, recommended a precautionary approach to the issue of mobile phone safety but did not find conclusive proof that the technology is a health risk. Several scientists are concerned that mobile phones pose a greater health risk than the industry admits. Dr Gerard Hyland wrote an article for The Lancet last November warning that mobile phone emissions can affect brain functions, and that young children would be at the greatest risk from any ill-effects. The mobile industry insists that there is no proof that mobile phones pose any health risk to the consumer. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet news forums. Let the editors know what you think in the Mailroom. And read other letters.