You must obtain a permit to carry, by going before a law enforcement panel. You must have a valid reason for the CWP such as, deposititing large sums of money in an after hours bank drop, death threats, your job requires it etc...Your cab company may have a rule against CW on the job to protect its self from law suits. But it depends on your state law. Some states horde Conceiled Weapons Permits. To apply they require you to be finger printed, schooled in the use of the weapon, and register the weapon. (if not already done) If you have any type of criminal record. (Not includeing traffic violations) Forget it! You wont get it. And you must pay for the school, permit fee's.
For more info visit NRA.com They should have a section with your state laws, and how to obtain one in your state.
Good luck!