There's total chaos in store on Saturday for anyone with an older, clunkier mobile phone. A smaller chaos lies in wait for people whose friends have older, clunkier mobiles.As of midnight on Friday all mobile numbers starting 03, 04, 05, 08 or 09 will simply cease to work. They will all be changed to 07 numbers as far as the network goes, but what numbers are stored on your phone will be another matter. However, Carphone Warehouse is riding to the rescue. The company has set up a quick fix, available to anyone who calls in at a Carphone Warehouse store to have their SIM card updated. The mobile seller estimates that there are 12 million people with the old numbers and that people up and down the UK have a total of 400 million old numbers stored on their mobiles. It says its free service will save UK mobile phone owners 90 million reprogramming hours. But the company isn't taking on any extra staff to cope with the demand. A spokesman said: "As it takes such a short time, shorter than a sale, the normal staff will be able to cope." For people who can't make it to a Carphone Warehouse, The Big Number - the quango set up to deal with the chaos - will have a team of hundreds to tell you what the new numbers are if you dial freephone 0808 224 2000. Or you can look it up on http://www.numberchange.org . While doctors and hospitals will also be affected by the change, due to an increasing reliance upon mobiles and pagers for medical staff, a strange quirk of priorities will see the sex industry's '08' and '09' prefixed premium rate numbers escape the chaos of the transition. Companies running sex lines will keep their current numbers and as such will avoid the massive costs of re-advertising their services.