Cab Drivers and Cell Phones

Do cab drivers have some ultra-cheap cell phone plan that no one else knows about? Those dudes are on the phone ALL THE TIME. Are they running a multi-national corporation from the driver's seat? Are they live-broadcasting their big city experiences back home to their native country? How is their phone bill not $800 per month? It really doesn't make a shred of sense how they can do it, but they do. And not just talking, people are calling too. They hang up and within 10 seconds their phone is ringing again. I remember a long cab ride I took and the driver got four separate calls. That was an extreme case, but I'm telling you that this happens all the time. Who could these people possibly be? It is truly one the great unsolved urban mysteries.