A driver’s number or call sign can be very important to him; some drivers want their lucky number or a number that means something significant to them. This leads to drivers trading numbers and even in some cases swapping firms if they can’t get the number they want. A while back one of our local drivers swapped from number sixty-one to number fourteen because he said "it was too many syllables in sixty-one for him to say on the radio."
You will find that not many taxi firms have a driver thirteen; I guess you will think that we are a superstitious lot, but round here thirteen is reserved for a call for help. So if you hear your driver shouting thirteen and giving his location you know that you have really spooked him and that you will be surrounded by twenty bloodthirsty cabbies within minutes.