It depends on the hours you do.
I have an uncle who works three nights a week taxiing. But those are three 14 hour nights, from 6pm til 8am, thursday night, friday night, saturday night. He doesnt work at all between sunday and thursday.
Its a dirty messy business working nights only, there is enough work for him to do it but he really deals with people in the worst of conditions, he has been threatened, attempted assault, robbed, taxi vomited on and in, people passed out etc...
The competition is fierce since deregulation (He drove a taxi prior to deregulation). He claims over and over that its a young mans job, but he still does it. He doesnt have to work past his assigned hours because he owns his taxi plate and car so not working to pay rent to someone. The down side of this is that he pays all costs on maintenance of the car. I dont think he is with a radio company either - as far as I remember he doesnt bother because he only works nights.