There is no longer a taxi faction, it is now a job. You have to visit the main headquarters located in Montgomery and /getjob there. Once you obtain the job navigate to the garage where you will find the taxi vehicles. For the commands type /help job.
The taxi job became a sidejob, once you become one in the Montgomery Taxi Depot, you have acces to the garage where the taxi's are parked, you can pick one and go on duty, receiving calls and respond to them.
You go to the HQ in Montgomery and you go inside, afterwards getting the job OOCly. Then you go to the garage and tell /onduty, (Or what it is) then you'll have to wait some time, then people need a taxi. So after around 3 jobs there's nothing to do. So it's like a sidejob. But no one need it anymore. It's boring like hell