By Jonathan Fildes Science and technology reporter, BBC News In the aftermath of the 7 July bombings, people were understandably keen to talk on their mobile phones. Londoners wanted to assure friends, relatives and colleagues that they were OK; keep up to date with the latest news or find out whether anyone they knew had been caught up in any of the four explosions. Yet, while speaking on a mobile phone is a routine part of modern life, for a crucial eight hours on 7 July it became difficult, and for many, impossible. In some areas of London, the sheer number of people wanting to make phone calls was enough to bring the mobile networks to their knees.